there's probably more information here than you need -
but maybe this can help get you started....

first, you will want to clear the vines from your "keepers" - shrubs and trees.
and you want to be able to identify invasive species in your area and get rid of those as well.
if you are pulling out large patches of invasives, you may want to look into spreading some seed, or filling in with plants. otherwise you might find yourself pulling up multiflora rose, only to come back next year to a patch of garlic mustard.

I don't know how overgrown it is, but you may want to do some "pathkeeping", too.
after these basics are done, I find that the garden will kinda tell you where to go next.

there's great information here, and other online sources. get a list of invasives in your area, and try to familiarize yourself with them. a good guide book would help, too.

you'll be doing a lot of subtracting - if there's something you cannot identify,
I suggest leaving it for now. you can take photos and try to identify them later,
but there may be something native and desireable growing.

here are some threads from the garden forum and the search words I used to get there.

some tips to get you started.....

clearing woodland:

http://forums.gardenweb.com/forums/load/woodland/msg071110068318.html

http://forums.gardenweb.com/forums/load/woodland/msg0317183118236.html

http://forums.gardenweb.com/forums/load/woodland/msg0402262725394.html

http://forums.gardenweb.com/forums/load/woodland/msg071436024378.html

http://forums.gardenweb.com/forums/load/woodland/msg07140337930.html

neglected garden:

http://forums.gardenweb.com/forums/load/newgard/msg0813524910737.html

http://forums2.gardenweb.com/forums/load/design/msg0610583824814.html

overgrown garden:

http://forums.gardenweb.com/forums/load/newgard/msg0813524910737.html

http://forums.gardenweb.com/forums/load/newgard/msg0813524910737.html

(sorry, I tried to make the links clickable, but it wouldn't put the message thru ... if you do want to check out the links, you'll have to copy them, and paste them into the address bar)

good luck!

Bubbleoffplumb's response sounds right to me. I have been clearing invasives for over four years and have found that they have an amazing potential to rebound. However, things are still much better than they were four years ago. You will have to find the right mix for you that is part clearing invasives, part path-making, and part adding and encouraging desireable plants. It is usually correct to start with clearing vines off of your desireable plants (especially mature trees and shrubs that simply cannot be replaced with purchased specimens) since you will want to have those things that are already there (and that have proven their ability to survive on your land) to do some of the fighting for you. For vines: cut low, cut high, remove the cut section and leave the rest to dry out and crumble in the canopy.
Some helpful resources for info on invasives are The Nature Conservancy and the Invasive Plant Council of New York.

Since we are both in New York (which has been importing invasives since colonial days) I can tell you to beware of:
- oriental bittersweet [vine]
- porcelain berry [vine]
- mile-a-minute [vine](but I don't have this one fortunately)
- english ivy [vine]
- multiflora rose
- winged euonymus
- creeping euonymus
- japanese honeysuckle [vine]
- garlic mustard
- mugwort
- ailanthus trees (tree of heaven)
- norway maple
- most honeysuckle shrubs
- phragmites
- bamboo
- japanese knotweed

There are others I am forgetting but these are some of the worst.

I have also spotted Kudzu in Queens recently but have yet to see it elsewhere in the State.