Ok im only like on ch4 and i feel like i should sell some stuff im picking up but then again im also afraid to because i don't know if it will be used for something else later on, any tips on what i should do?

sell all of your pheonix downs. you dont need those things

First off, Credit Chips, if you haven't figured that out, I knew it took me awhile to do so.
 
Secondly, gear you don't plan on using.  I may wind up eating those words later when I find out I need all of Lightning's weapons, but I needed cash so I sold all the ones I wasn't using.  If it's already in the store for sell and you don't plan on using it, definitely safe in selling it.
 
Also, what do you want to buy by Ch. 4?  Most of the stuff you can get by finding chests.
 
Save your moneys.

" First off, Credit Chips, if you haven't figured that out, I knew it took me awhile to do so.  Secondly, gear you don't plan on using.  I may wind up eating those words later when I find out I need all of Lightning's weapons, but I needed cash so I sold all the ones I wasn't using.  If it's already in the store for sell and you don't plan on using it, definitely safe in selling it.  Also, what do you want to buy by Ch. 4?  Most of the stuff you can get by finding chests.  Save your moneys. "

i don't want to buy anything but i keep picking up stuff from the fights and im like wtf do i need that stuff is it all trash and is there a mix of like junk or stuff i need? after posting this i just go to the part where explanes the upgrade system so :D i guess i figured it out and thanks for the reply

" @Diablah: Most the components you get from mobs are used for upgrades, I sold mine without even realizing it (curse you FF12 for teaching me this!) so yeah I was pretty annoyed when it came time to upgrade gear. "

Not that trophies and whatnot are a big deal, but If you happen to be trophy/achievement hunting, just don't sell the low level elemental rings (i.e. ember ring, frost ring, aqua ring, etc.) The treasure hunter trophy/achievement requires you to own each item in the game at least once, but upper level elemental rings can only be acquired by upgrading from the lower level rings, which you find in treasure chests, but never in shops.  If you sell them you'll never get a chance to re-buy them again to start the upgrades.  The only other way to acquire them is by maxing out and dismantling elemental charms (i.e. Fire Charm, Ice Charm, etc.), which can also only be acquired once from treasure chests in Chapter 11.  So don't sell those either.

Don't sell anything. What do you need gil for anyways?

I sell most of my components to buy the specific ones I want (colored jellies and perfect conductors).  I tend to sell the rest to just focus on those.  
 
Don't sell your weapons/keep one of each accessory at least if you want the treasure hunter trophy, some things can only be acquired by upgrading the lower level stuff.  I sell duplicate accessories and excess components, plus the items meant for selling like credit chips, incentive chips, and ingots.  Probably should keep your minerals too, you need those to upgrade a weapon from tier 1 to tier 2 (to upgrade a weapon to tier 3 requires either a 2 million gil item or a rare drop from an annoyingly hard enemy)
 
Money is always hard to get in this game, just the way it is.