If you're talking about honing (straightening the blade so that the sharp end points outwards and is available for work) rather than actual sharpening (removing some of the blade so that what's left is at an acute angle), you can hone even the cheapest of disposable blades and razors on a towel or a pair of jeans. Dry the razor thoroughly after each use, then rub it over the fabric in the opposite direction to how you shave. Should get you at least a few more good shaves out of each blade.
The only actual shaving tip I have is to use oil instead of soap. When your beard hair is wet, put a dime-sized glug of oil (like olive oil) on your palms, rub them together, then rub them all over your face. Shave as usual. Smooth. Maybe not quite as close as foam, but not far off. Also much easier to take along a wee container of oil when you travel, maybe in an empty hotel shampoo bottle.