That's a pretty broad question... In general, the first decision is whether or not to start over completely. If there are sufficient components of the native system left, you might choose to try to suppress invasives with spot-treatment and/or selective herbicides, prescribed grazing, or other techniques and maybe also overseed or otherwise enhance the native plant community. If, on the other hand, the system has essentially flipped to a completely new system, it might be most effective to just kill it all over and start again. This is clearly not a decision to be made lightly, but in some cases it is more cost effective (and simply effective) than trying to fight a constant losing battle against dominant invasives.