My version, not sure what you are meaning by ショートフォーム, I translate from short form. It's far from perfect, but it's quite hard to translate simple sentences without context when not used to.
Maybe へた would be better than じょうずじゃない but doesn't へた imply that you are awful at it?
Haven't learned ほとんど but is probably better than すこし. Totally forgot about あまり, makes a lot more sense..
As for the last one, Short forms is the 'informal' conjugations よみません > よまない , たべます > たべる.. so I was trying to write all my sentences into short/informal speech (with particles though).
I wanted to say "I want to get better at Short Forms" so is the とおもいます necessary?
Thanks for your help!