Put a helmet
Thousands of people arrive each year to the emergency room because they didn't put a helmet on and got hit in the head. Try to pick a Helmet you like visually and that fits perfectly.
Choose the right bike for your body
Every bike comes with different measurements and 'body' structure. Pick up a bike that you sit comfortably on, with enough room for maneuvering and efficient and flexible riding.
Start riding slowly, carefully, until you feel comfortable speeding and start tearing the city up :)
Merge into traffic
Be smart; if your are in on the road or beside it, you are a part of traffic and you should ride only where you are visible to the other drivers on the road.
Keep your shoulders strait and up
If you really want to keep you powers and avoid tiredness, it is best to keep shoulders up and every couple of minuets mover the entire shoulders and neck area for easy and fast release.