One of the problems with crawl spaces is no or poorly installed footing drains. Even though in some instances they are not required i always install one when I can. Another problem we see is in the types of venting in the crawler. Old style was to cut into the rim joist 14"x8" in btwn the joists. problem is that inevitably when insulation contractor shows up, they place insulation to close to vent, blocking good air flow. New IBC call for R-30 in floor systems which if you are on top of it requires either a 2x12 floor joist or a 11 7/8" TJI style floor joist. Otherwise the insulation hangs down below say a 2x10 or 2x8 joist. The best method is to place vents in foundation prior to pouring to vent "below" insulation and floor. Mechanical vents can be placed on a humidistat which can be set to turn on vent fan when humidity reachs a certain level. ($25.00 Home depot, available next to the attic fans display). Also, make sure to use 6-mil black poly vapor barrier. the absolute best. Make sure any and all wood debris is removed also. cheers.