Yeah I agree about cleaning it up.  Right now it barely qualifies as pixel art and not just some rough drawing.  Also don't use the same boring preveiw (sic) image for all your pieces, makes them real hard to distinguish between when listed.  Use a bit of the actual image or at least something that relates to it.

first of all, its spelled p-r-e-v-I-E-w .. not preveiw ;D.... 

this and also the jurrasic park jeep look kinda like traces too me,... anyhow.... the lines are very jaggy.... clean them up ... also id say u rly should shade this and maybe add some little background aswell