Your Tools of Destruction
There are several different weapons found in Ratchet and Clank Future: Tools of Destruction. They all have their uses, but for the most part, you can focus on a small number of them and make it through the game. All are upgradeable, both in level and in abilities, and you should do this as quickly as possible with the weapons you want to use the most. To upgrade a weapon's level, all you have to do is use it. Since you can go back and play previous levels several times, this is a great way to level up weapons that seem too weak to use, as well as pick up a few extra bolts, required to purchase new ones. To upgrade a weapon's abilities, you will need raritanium, found in various treasure chests and from defeating enemies. Here are some of my recommended weapons of use:
The Combustor - You begin the game with this weapon, and it may seem weak as you start to take on harder enemies. However, it has a large ammo capacity, and also can be upgraded to shoot three bullets at once (only using 1 ammo per shot still). Another advantage is the ability to get raritanium from enemies. You have to purchase this as an upgrade, but not all weapons have it, so especially early on, use the Combustor as much as possible in order to power up all your weapons quickly.
The Negotiator - Not just a movie with Samuel L. Jackson, this rocket-launching beast is a fine addition to your arsenal. One of the most powerful weapons in the game, especially after upgrades, it can take on regular and shielded enemies with ease, and should quickly become your favorite against bosses.
Nano-Swarmers - These may seem weak at first, but after a few upgrades, there's nothing better to take on groups of enemies. Deploy these turrets, then run and hide. You can have up to two active at once, so keep these by your side to avoid being overwhelmed. Against bosses, or in the arena, they are also quite useful, and can do a decent amount of damage while you try to gather more ammo.
Mag-net Launcher - Perhaps the most underrated weapon in the game, this will temporarily suspend an enemy's movement, and hurt him as well. Great to use to freeze enemies while you pull out another weapon, such as the Combustor, to get extra raritanium.