There are 55 Ways of life including the starting one. In order to unlock a Way of Life you need to attain a very specific combination of titles (listed below). You can check which Ways of Life you have unlocked by going into the officer creator, then when you create an officer you can select one from all your unlocked Ways of Life. I used a Notepad document and wrote down the Ways of Life as I got them to avoid having to do this every time I wanted to check what I had, but if you are uncertain which ones you have this is a good way to check.

IMPORTANT: For the game to recognize that you have completed a Way of Life, you MUST save so the game can save it to your System Data. You do NOT need to complete the scenario with the Way of Life for it to count. You just need to save.

Definition of the tiers: If you want a Way of Life that is a lower tier (tier 0, being the lowest) or equal, then you can't get it without starting a new game or reloading an earlier save when you had a lower tier Way of Life. Example: You are an "Undefeated Veteran" (Tier 15) and you want any of the Ways of Life that are tier 15, such as "High Spirited Commander", or lower. You can ONLY move up tiers.
Example: Tier 0 --> 2 --> 8 --> 12 or Tier 0 --> 1 --> 2 --> 3

Tier 0:
Ordinary Man - default way of life

Tier 1:
Many Faceted General - Complete 1 raid quest (Desperado)

General Amid Chaos - Complete 1 infiltration quest (Stealth Shadow)

Loyal Warrior - Complete 1 extermination quest (Mighty Warrior)

Calm Traitor - Complete 1 assassination quest (Silent Blade)

Tier 2:
Raging Commander - Win 1 Invasion (Experienced General)

Tier 3:
Precise Intellect - Win 1 Defensive battle (Armored Warrior)

Tier 4:
Pinnacle of Splendor - Have 99,999 or more gold (Flowing with Funds)

Tier 5:
Humble Retainer - Spend 3 years as a Free Officer (Lone Wolf) and rest 5 times (Easy Going)

Tier 6:
Loyal General - Win 5 Defensive battles (Solid Fortress)

Tier 7:
Wandering Warrior - Transfer kingdoms 3 times (Constant Traveler)

Tier 8:
Rising Star - Get a large promotion from being a Free Officer (Sumptuous Indulger)

Tier 9:
Heroic Unifier - Have 99,999 or more troops (Endless Numbers) and have 15 or more regions under your control (World Conqueror)

Tier 10:
Unprincipled Thug - Virtue of -1000 or lower (Violent Rogue) and perform slander 1 time (Shyster)

Tier 11:
Lord's Right Hand - Successfully negotiate 1 or more diplomatic treaties (Double Dealer) and have your opinion adopted 1 time during a War Council (Muckraker)

Tier 12:
Elite Warrior - Have 10 or more regions under your control (Regional Powerhouse) and have 3 or more regions that are happy (Benevolent Ruler)

Tier 13:
General of the Land - Have 15 or more regions under your control (World Conqueror) and don't lose a single territory for 2 years (Great Empire)

Tier 14:
Devil May Care Warrior - Increase Virtue by 1000 or more in a single year (Repentant Vagabond), decrease Virtue by 1000 or more in a single year (Corrupted Husk), and achieve both Virtue above 3000 and below -3000 (Two-Faced)

Tier 15:
Undefeated Veteran - Win 5 defensive battles (Solid Fortress) and complete 3 escort quests (Master Defender)

High Spirited Commander - Win 5 Invasions (Victorious Commander) and have 10 officers with high friendship with you (Likeable Fellow)

Tier 16:
Trustworthy Hero - Complete 1 escort quest (Rock Solid) and have 10 officers with high friendship with you (Likeable Fellow)

Tier 17:
Honest and Handsome - Be asked by other officers to join their kingdom/vagabond units 3 times (Well Rounded) and have women confess their love for you 3 times (Stunning Beauty)

Fair Flower - Be asked by other officers to join their kingdom/vagabond units 3 times (Well Rounded) and have men confess their love for you 3 times (Divine Countenance)

Tier 18:
Stormy Life - Start a rebellion/betrayal and be defeated (Defector), spend 5 years as a Free Officer (Free Spirit), get a large promotion from being a Free Officer (Sumptuous Indulger), and successfully rebel as a Strategist/Marshall (Usurper)

Diamond in the Rough - Have 15 or more regions under your control (World Conqueror) and 10 or more years pass (Bellicose Warrior)

Tier 19:
Keen Eyed General - Have 8 or more regions that are happy (Peaceful Land) and successfully recruit others 5 times (Keen Eye)

Tier 20:
Immortal - Perform rest 10 times (Happy Go Lucky), spend 5 years as a Free Officer (Free Spirit), and 10 or more years pass (Bellicose Warrior)

Tier 21:
Life of Ups and Downs - Start a rebellion/betrayal and be defeated (Defector), have 50,000 or more troops (Vast Army), have 50,000 or more gold (Healthy and Wealthy), and spend 1 year as a Free Officer (Wanderer)

Tier 22:
Unmatched Under Heaven - Win 10 Invasions (Unstoppable) and complete 3 extermination quests (Proficient Fighter)

Tier 23:
Close Adviser - Be asked by other officers to join their kingdom/vagabond units 3 times (Well Rounded) and have your opinion adopted 3 times during a War Council (Shrewd Staffer)

Tier 24:
Unpredictable Schemer - Transfer kingdoms 5 times (Eternal Pessimist), start rumors 1 time (Truth Spinner), and win a battle with a difference in troop strength of 5,000 or more (Indomitable Valor)

Tier 25:
Unmatched Intellect - Don't lose a single territory for 5 years (Inimitable) and successfully negotiate 5 or more diplomatic treaties (Sly Fox)

Wiley Tactician - Successfully rebel as a Strategist/Marshall (Usurper) and successfully negotiate 5 or more diplomatic treaties (Sly Fox)

Tier 26:
Ruler of the Midlands - Conquer 5 regions within 1 year (Lightning Fast) and spend 1 year as a Free Officer (Wanderer)

Tier 27:
Outstanding Talent - Don't lose a single territory for 5 years (Inimitable), successfully recruit others 5 times (Keen Eye), and successfully negotiate 1 or more diplomatic treaties (Double Dealer)

Tier 28:
Benevolent Ruler - Virtue of 3000 or higher (Selfless Soul), have 10 officers with high friendship with you (Likeable Fellow), have 3 or more regions that are happy (Benevolent Ruler), and donate 5 times (Charitable Soul)

Tyrant of Chaos - Virtue of -3000 or lower (Diabolic Fiend), have 3 or more regions that are unhappy (Despot), accept 1 bribe from your subordinates (Ravenous Greed), and execute 1 person (Grim Reaper)

Tier 29:
Tall and Handsome - Win 5 Invasions (Victorious Commander), complete 5 escort quests (Guardian God), have 10 officers with high friendship with you (Likeable Fellow), have women confess their love for you 5 times (Handsome Man), and be asked by other officers to join their kingdom/vagabond unit 5 times (Unparalleled Achiever)

Seductive Beauty - Transfer kingdoms 5 times (Eternal Pessimist), complete 5 infiltration quests (Thieving Brigand), achieve both Virtue above 3000 and below -3000 (Two-Faced), have men confess their love for you 5 times (Perfect Looks), and be asked by other officers to join their kingdom/vagabond unit 5 times (Unparalleled Achiever)

Tier 30:
God of War - Win a battle with a difference in troop strength of 20,000 or more (Stalwart Veteran), win 10 defensive battles (Indestructible Fighter), complete 5 escort quests (Guardian God), and be asked by other officers to join their kingdom/vagabond unit 5 times (Unparalleled Achiever)

Tier 31:
Bold and Brave - Win a battle with a difference in troop strength of 20,000 or more (Stalwart Veteran), win 10 Invasions (Unstoppable), complete 5 extermination quests (Skillful Hunter), and have 10 officers with high friendship with you (Likeable Fellow)

Tier 32:
Flying General - Win a battle with a difference in troop strength of 20,000 or more (Stalwart Veteran), win 10 Invasions (Unstoppable), complete 5 raid missions (Pirate Pillager), and have 20 officers with low friendship with you (Mortal Enemy)

Tier 33:
Duplicitous Joker - Win a battle with a difference in troop strength of 10,000 or more (Dauntless Courage), complete 5 assassination quests (Bad Omen), start rumors 3 times (Rumormonger), and transfer kingdoms 5 times (Eternal Pessimist)

Aide to Kings - Don't lose a single territory for 2 years (Great Empire), successfully negotiate 10 or more diplomatic treaties (Strategy Master), have your opinion adopted 5 times during a War Council (Ingenious Schemer), and successfully make 5 alliances with other kingdoms (Compromise Seeker)

Unrecognized Genius - Don't lose a single territory for 5 years (Inimitable), successfully negotiate 10 or more diplomatic treaties (Strategy Master), spend 5 years as a Free Officer (Free Spirit), and get a large promotion from being a Free Officer (Sumptuous Indulger)

Unparalleled Strategist - Have your opinion adopted 5 times during a War Council (Ingenious Schemer), successfully use the scout command 3 times (Fast Talker), start rumors 3 times (Rumormonger), and successfully rebel as a Strategist/Marshall (Usurper)

The Little Conqueror - Win 5 Invasions (Victorious Commander), don't lose a single
territory for 2 years (Great Empire), conquer 5 regions within 1 year (Lightning Fast), fight with 2 other kingdoms simultaneously (Iron Fist), have 3 or more regions that are happy (Benevolent Ruler), and spend 3 years as a Free Officer (Lone Wolf)

King of Hanzhong - Have 15 or more regions under your control (World Conqueror), successfully recruit others 5 times (Keen Eye), Virtue of 3000 or higher (Selfless Soul), have 20 officers with high friendship with you (Venerated Friend), have 8 or more regions that are happy (Peaceful Land), donate 15 times (Generous Donor), and have 99,999 or more materials (Bumper Harvest)

Tyrannical King - Hold 3 or more parties (Party Animal), Virtue of -3000 or lower (Diabolic Fiend), have 20 officers with low friendship with you (Mortal Enemy), accept 3 bribes from your subordinates (Shameless Avarice), have 5 officers leave your own kingdom (Solitary Stead), have 8 or more regions that are unhappy (Oppressive Ruffian), execute 15 people (Cerberus), and have 99,999 or more gold (Flowing with Funds)

Hero of Chaos - Have 15 or more regions under your control (World Conqueror), conquer 5 regions within 1 year (Lightning Fast), fight with 2 other kingdoms simultaneously (Iron Fist), successfully recruit others 5 times (Keen Eye), achieve both Virtue above 3000 and below -3000 (Two-Faced), and have 99,999 or more troops (Endless Numbers)

Tier 34:
Great Authority - Successfully negotiate 10 or more diplomatic treaties (Strategy Master), have your opinion adopted 5 times during a War Council (Ingenious Schemer), successfully use the scout command 3 times (Fast Talker), start rumors 3 times (Rumormonger), successfully recruit others 5 times (Keen Eye), successfully make 5 alliances with other kingdoms (Compromise Seeker), perform invite 5 times (Luminous Recruiter), successfully use alienate 3 times (Deep Thinker), and successfully rebel as a Strategist/Marshall (Usurper)

Mighty Warriors - Win a battle with a difference in troop strength of 20,000 or more (Stalwart Veteran), win 5 Defensive battles (Solid Fortress), conquer 5 regions within 1 year (Lightning Fast), don't lose a single territory for 5 years (Inimitable), complete 5 assassination and 5 infiltration quests (Elusive Knave), complete 5 raid and 5 extermination quests (Raging Lion), and win 30 Invasions (Invasion Expert)

Virtuous Saint - Win 10 Defensive battles (Indestructible Fighter), complete 5 escort quests (Guardian God), successfully make 5 alliances with other kingdoms (Compromise Seeker), have 20 officers with high friendship with you (Venerated Friend), have 8 or more regions that are happy (Peaceful Land), Virtue of 9999 (Noble Saint), and donate 15 times (Generous Donor)

Fiendish Beast - Win 10 Invasions (Unstoppable), complete 5 assassination quests (Bad Omen), start rumors 3 times (Rumormonger), have 3 or more parties (Party Animal), have 20 officers with low friendship with you (Mortal Enemy), accept 3 bribes from your subordinates (Shameless Avarice), have 8 or more regions that are unhappy (Oppressive Ruffian), execute 15 people (Cerberus), Virtue of -9999 (Wolf in Sheep's Clothing)

Tier 35:
All Encompassing - Complete 5 assassination and 5 infiltration quests (Elusive Knave), complete 5 raid and 5 extermination quests (Raging Lion), and win 30 Invasions (Invasion Expert), win 20 Defensive battles (Defensive Ace), successfully negotiate 10 or more diplomatic treaties (Strategy Master), Virtue of 9999 (Noble Saint), Virtue of -9999 (Wolf in Sheep's Clothing), transfer kingdoms 5 times (Eternal Pessimist), spend 5 years as a Free Officer (Free Spirit), and 30 or more years pass (Battle Expert)

Credits:
http://www.trueachievements.com/a198093/many-ways-to-live-achievement.htm#