Sanding down an old finish (unless you are taking off a lot of material, like on a floor), is possibly the worst way to do it.

- You will clog up a lot of sandpaper and spend a long time doing it.

- You will not get all the old finish off and risk having an uneven staining.

- If your table top is veneer, it is a real risk that you will sand through it in some places before you know it.

Bite the bullet, get a chemical stripper, some gloves, eye protection, and a putty knife. Find a shady area outdoors, apply the stripper, walk away and let the stripper do its job and come back and scrape off the old finish.

Neutralize or rinse as directed by the can of stripper. Let it dry for a couple of days. Lightly sand, just enough to remove the fuzzies. Then apply a stain and finish of your choice.

Here is a link that might be useful: finishing for first-timers.