Veneer faded from sun  

Thicker than a playing card?
Probably start with P240 and skip every other up through the grades to P400 for varnish or P600 for oil finish. Use a 1/4 sheet hand block, either hard or semi-hard (like cork), but not soft. Change to fresh paper often. Work with the grain, and be careful not to round-over the edges until the last step, if they're too sharp.
If you're at all apprehensive, you could start with P320.
A pro might use a card scraper, but if you're not good with one, I'd avoid it.
Bon chance!
Grading cross-reference:
http://www.woodturners.org/tech_tips/misc-pages/abrasive_grading.pdf

Yago,
My experience with...
Yago,
My experience with sun damage is that it's going to be nearly impossible to completely remove by sanding alone.
Obviously sanding away the upper layer of the veneer will help, but the damage usually goes pretty deep, deep enough that it becomes dangerous to continue sanding away.
Good luck!

This may be sacrilege, but...
This may be sacrilege, but if it's an oiled piece you could apply oil and then onto the oiled surface, wipe on an alcohol based stain (which will dissolve into the oil) to try to match the top to the rest of the piece. Or separately mix into a pot of oil some stain and then apply.
This worked well for me on a no-name teak sideboard that had been sanded too vigorously in one area.

If it's reasonably evenly fad...
If it's reasonably evenly faded I would just try a light tinted brown wax, theres a few available, build it up until the colour matches then wax the whole thing with neutral.

Lovely sideboard! How much did you pay if I may ask?

There is a trick
I use on items like that.
Wet n dry paper and then sand the area starting at 320 grain working your way up to 400.
Do not remove or wipe away any of the residue and oil as you sand but leave this on to soak back into the wood.
Once you a happy with the feel of the wood after the 400 grain leave it to dry completely until you have the sanding residue form a coat on top.
Rub it now with an old nylon soft pad to remove the residue and hey presto you have a beautiful surface with a matt oil finish.
The oil and residue will have feed the veneer and brough some of the colour back.
For really bad fading you may need to dye it again but thats a different story where you have to mix sample dyes until you get the best match.

Thanks for all the tips...
Thanks for all the tips everyone. I think I'll try Simon's method, it sounds very interesting. Will post results, might be a while as the sideboard's in storage now (I need a bigger place!).