First of all you have to unlock until rank 50 in Arena, to do this you should have a save just before facing the last boss of adventure.

Now prepare your hexes (I recommend the blue ones) because you will need to fill at least 250 spaces.

First in floor 4 you have to connect the terminal near Hughes Power Station with the Elevator to level 6 and the Arena.



On level 6 you have to connect the elevator to level 4 with the two terminals near to Patertopolis.


All those terminals will give you 1.5 drop rate, 1.5 exp and the third one will double the effects of the other two.

Now equip the mulets of extra drop rate and exp to all your characters and go to the Arena.

If you have come from the console versions you will notice that the exploit of buying and selling an item in a specific place have been remove so you now have to work in order to get more money.

To get money quickly you need an item that give you a good quantity on money, but also are easy and fast to obtain. So you have to go and kill dogs. Why?
Because the dogs give you meat, and meat (normal, quality and luxorius) give you a lot of money and also the dogs are in very low levels and are very easy to kill.

So go to Arena and kill animals en Rank 25, 26 or 30 whatever you think is faster or easier for you.

Here is a video from another author of that part in arena

As you already know for this moment you have to level up 3 things: Guns, SMG and Grenades.
In order to get experience you have to do direct damage to the opponent (shields dont give exp!) and the experience you get is proportional to the quantity of HP you remove in one hit.
So in order to get more exp you have to full scratch the enemy HP (make all the HP bar blue) and kill him with one single hit with the weapon and character you want to level up.
For this mission we will need to kill enemies with very high HP but that are easy to kill, and also by the nature of the enemies leveling up SMG will required different monster than for guns and grande ones.

Guns and Granades:

The most efficient way is to do Arena rank 45-3. There you will find the turrets cannos, etc and every one of them will have from 40k to 60k of HP. However, all the levels of rank 45 have almost the same monsters, the 45-3 is known for has more of them.

The advantage and disadvantage of those monsters is that you only have to destroy the shields in order to kill them, so is an advantage because with smg you could destroy the shield with one compleate charge of smg, but disadvantage because this only works to level up guns and granades because you will never do scratch damage to the monster life.

Here is a video from another author that show the procces in rank 45


SMG:

In case of SMG you also want an enemy with plenty HP but not lot of shields. The enemies will be the Soldiers AN and GA from Arena rank 46 and 47, each one will have at least 20k HP.

I recommend to do the rank you are most comfortable with, they are not as easy to kill as the rank 45 monsters, but besides Neverland and bosses are the enemies with most HP that give SMG exp.

In this case I dont have a videos, but they are like the soldiers you could find in the Basilica, and are even easier.

Those are the most hard to advice ti farm because there are plenty of types of eachones that I cant say an specifict place to get all.

Hexes:

If you are in the last chapters you have realize that a very easy way to farm them is from the random battles in lower levels, more specifict battle agains human enemies (mafia boys), however maybe you are searching for one color in specifict, in this case the only way to farm them without moving from elevator to elevator is in the arena. First you have to check the bestiary (the shinning book in your home or near the mission board), go to human enemies and find the one that drop the color you want, then inmediatly go to the arena and kill them (always with increase of item drop equipment).

Breaking Shields and Bonus Shots helps to get some extra drops.

Wepon Parts:

The only way to get weapon parts are from mission rewards or crafting them. Despite the variety of parts that are to craft only few are really usefull in late game.

Your weapon should look like those



You notice that alot of the parts are repeated, that is because those are the most useful parts (best conections). So you always have to focus on craft them, but the case is that the materials sometimes could be hard to figure where are.

Once you unlock all the recipes (in last chapter, talk with the NPC that craft parts in all the cities and check the new ones, this will automatically unlock the recipe for the NPC who craft in the main city) check for the material needed, search the enemy who drop it in the bestiary, and go to the Arena.

The material to craft those high level parts are usually drop from tanks and helicpters, check the mechanic enemy section in the bestiary.