GET 3 SCULLS RATING IN EACH LEVEL AND EACH WORLD
Hardest (yet still very easy) type of achievements in this game. Requires you too beat you each specific level and every world without having a single enemy reach the scene. If you missed even one enemy, restart the level immediately so that you don't have to replay it later.

The tips and tricks to achieve it:

• Know the best towers (i don't know their english names so i will write their price instead):
  1) First tower (400/600/900) is good at beginning when you have no money and you need to cover bigger area. Sell it later to replace it with something more powerful;
  2) Omni (1200/1800/2500) is the best tower in the entire game. Use it to replace First tower when you have enough money to buy and immediately upgrade it to 2lvl. Max priority for placement in corners and between roads, but later you can put those all over the place;
  3) Freezer (400/600/900) - no much use, but it's cheap and in few levels it's a musthave when enemies are getting too fast;
  4) High Tower (900/1400/2100) - you can put one tower close to the scene just in case, when you already have a lot of money, so stronger enemies are always getting damaged by its fire;
  Other 4 towers are inferior and underperforming.
  
• At the last wave you can sell towers enemy already have passed to buy/upgrade towers closer to scene;
  
• Don't forget your band can do a shockwave special to damage mobs and Bosses, use it to safe yourself when enemy getting through your line of defence.

USE SPECIAL ATTACK x50 TIMES
Just don't forget to click sometimes on your band to release the shockwave, you can do it more than once per level. It's very useful for getting 3 scull rating on levels, so you probably will achieve it without even trying.

BUY AND FULLY UPGRADE EACH OF 8 SPEAKERS AT LEAST ONCE
Since you can beat most levels with just 2 types of speaker (Stock and Omni), you can pick 1 or 2 inferior speaker once for just one level just to get related achievements, and then repeat it for all the speakers left. After upgrading it to the max level you can forget about them.

Better to do at second world (country music), in first world you may have not enough spare money.

SELL A TOTAL OF 20 SPEAKERS
The only thing you have to rememeber is you are able to sell speakers at all.
You can sell towers after last wave during winning animation and that still will count.

AS YOU COMPLETING THE GAME YOU WILL ACHIEVE THOSE WITHOUT EVEN TRYING

• Defeat 1000 enemies;
  
• Defeat every type of enemy (4 types per each of 4 world) x100 times;
  
• Defeat every type of Boss (one type per each of 4 world) x10 times;
  
• Accumulate 20000 coins single stage (you can sell your towers at the end to achieve it earlier);
  
• Accumulate 100000 coins