I wrap all my bars starting at the stem with the roll of tape coming toward you (if you're on your bike) as you pull it under the bar. Much cleaner look w/o the electrical tape plus once the tape starts to fray at the turn of the bar, the rest is ready for replacement anyway.

One more thing, since bar tape is sold to cover drops, you have a lot more than you need. I like to wrap the turn forward with extra overlap to use up the tape and create a cushy spot in the spot where i put the most weight on my bullhorns.