can you post a pic of the trim youre referring to? i have an 08 4runner & it doesnt have any silver trim on the upper doors, its all black.

as for painting, its pretty much the same for any part, the prep is the key to getting good results. basically you want to clean the part to remove any dirt, grease or wax residue, dawn dish soap & warm water, then dry & follow up with rubbing alcohol on a clean rag. next scuff or sand the area, if you dont need to remove old paint then just use a red or green scotch brite pad or fine 400-600 grit sand paper, then wipe again with rubbing alcohol & be sure to wipe or blow away any lint or debris, can use a tack cloth too as the final step.

then use 1-2 medium coats of a good primer & allow to dry according to instructions on the can.
then spray the paint, 2-3 light to medium coats are best with the final coat more of a medium heavy coat to get a smooth finish but be careful not to do it too heavy to get runs in the paint.
when spraying do even strokes spraying past the part at the end & before the part at the beginning of each stroke, goal is to not start the spray in the middle of the part. you can also do 1-2 coats of clear in the gloss sheen you prefer, gloss or matte.
this is for spray cans, but you can always use a better quality paint in a gun with a compressor but you usually need some practice or experience to get a good spray pattern.

you should be able to get very good results doing those steps. best of luck!