WD-40 is a terrible idea! While it might help the usb port work better for a while, it will actually leave residue including anything it dissolves. Compressed air won't hurt, but it won't help much either. Isopropyl alcohol probably isn't the worst thing you could use, but it isn't ideal. For one, it's just a liquid, which isn't the best for cleaning hard-to-reach areas like micro-usb. It's conductive, and less than pure (ie, commercial) concentrations of isopropyl will actually have a percentage of water and take a long while to evaporate, not to mention that it's a less than ideal solvent. Also, I'm not sure if this applies to any cell phones at all, but "some" plastics can be critically weakened by isopropyl.
Fortunately, they actually make a substance for just this purpose. It actually combines the best parts of isopropyl (volatility, leaves no residue), wd40 (very good solvent for cleaning), and compressed air (comes in pressurized spray can). It's called contact cleaner, and it works magic on wonky USB ports, scratchy knobs, etc. Highly recommended, especially over the alternatives. Mine is radioshack brand ("Control/Contact Cleaner and Lubricant") but you can also find it online. DeoxIt is a major/trusted brand name for the stuff.