A passing fad in MotoGP and Superbikes but a motorcycle with rim tape can still look good can't it? We recently taped a rim with reflective rim tape, making the motorcycle more visible in the dark too.
Get the rims spotlessly clean, free from any grime or grease and completely dry. I'd wash, rinse and then use an alcohol-based cleaner, which will clean up and evaporate quickly. Some dedicated 'wheel cleaning' products are oil-based and may not help the tape adhere.
Best done with the wheels (both of them) up on a stand because the job's easier when you can spin the wheels. It can be done without but you'll need some help to hold and move the motorcycle. Another alternative is taking the wheels out and getting them inside but in that case make sure the wheels are flat and held down well. Some rim tape kits come with a plastic guide which can help keep an even keel, the easiest of all are pre-formed the right shape. If it doesn't don't worry, you just need time and care.
The trick is to get yourself in a fixed position and apply the rim tape in a consistent, mechanical way. Use one hand to hold the roll of rim tape (your middle finger), the forefinger and thumb to pull and remove the tape backing as you go and your little finger to act as a guide on the rim itself. That leaves the other hand to press the tape on the rim and alternately to move the wheel.
It's best done on a warm day in a garage to get the rim and rim tape to stick best. Borrow your girlfriends hair dryer to pre-heat the rims for a while before you start.