You really have to go one at a time and see if there's any problems. The first thing is to clean your tape path so you know that any residue is from the tape you just played. I usually start by zeroing out the tape counter and keep a little pad to note any weird noises or drop outs. Sit close enough so you can hear any untoward noises as the tape releases itself from the pack. You should have some spare 7" plastic reels ( I usually buy a 5 pack of low torque and regular hub reels from US Recording Media,..cheap) in case any are damaged and flanging (tape scraping after playing both sides). If the reel was real dusty, clean out the insides before playing side two ( I have a shop vac that I hook up as a blower, it just takes a couple of seconds but hold on tight!). If there's any loose dirt/dust in the box, clean that out with a regular vacuum with a brush attachment. As far as the boxes go, if it has a glossy finish, just try distilled water and clean rags. If it's a matte finish (like that Barclay-Crockers) I just dust the off and live with it. If the reels or boxes have scotch tape residue, there's a product called "GooGone" spray gel (it's not really a gel. I'd sue 'em for false advertising but it's made by "Magic American Products" and I wouldn't want to be turned into a frog or Donald Rumsfeld or something) and it works great for sticky stuff removal (you can get it at most super markets). For the tapes I really want to preserve, I also use a plastic slip cover over the box (never inside, if any of your tapes have inner bags, bury them at the northeast corner of the Foster Freeze just outside of Valley Forge. If only Washington's men had know about that spot!) I guess one of the main things to do is to play them. A few of the bad things that happen to tapes is exacerbated by not being unwound for decades. Also, you don't want to go to the trouble of cleaning the box up all nice if the tape is trashed or just plain awful.