I polished my 3L UIM and TB so far, but I'd steer away from polishing your MAF. Unless you can gut the MAF, you're going to subject the internals to very high heatfrom the polishing and extreme vibrations.
BUT, if you want to give it a shot.....
The MAF should have the ends sealed off to keep crap out of it. I'd put a clean shop rag in each side and then tape each side off.
In general the MAF is in fairly smooth shape and doesn't need the courser grits, so I would start off at either 400 or 600 3M wet/dry. With each grit, you MUST sand evenly and completely because if you rush it and go through grits too fast you will leave low grit scratches in and it'll look like ass. So to avoid this, take youtr time to make a quality asthetic mod because nothing looks worse than something done half....hearted
400, 600, and finish with 800. This is where a Craftsman buffing kit that you can get at Sears for like $15 comes in handy. It comes with 3 wheels and 3 compounds. The rule is never use more than one type of compound an any one wheel. You want to use the small with the course, medium with the medium and large wheel with the final polishing compound.
First is the course compound which is black or the emery compound, which can be used to smooth out the whole thing even more, taking the 800 grit "scratches" (they're so fine, it's hard to call them even that

) out.
Second comes the red buffing compound, which will polish it out a lot and will almost look done.
Finally, the white finishing compound to make that thing shine. To add that extra nice mirror finish.....use a aluminum polish, I used Mother's brand aluminm polish and some elbow greese.....
watch that drill chuck from knicking your MAF....I did a few times when doing my UIM

Nothing is worse than having to go back 4 or five steps to fix small things like that!
A lot of it is in compound usage and buffing technique. Look into Eastwood company for hardcore buffing/polishing equipment. They also have a good polished item clear coat that is good up to 300*.....they recommend against using it on exhaust manifolds so i think a UIM, TB or even the MAF should be fine.
Any other questions....ask away.