I commute to work every day in Tampa, FL a total of 13.2 miles round trip. Quite a few things I have learned over the years cycling in 4 states and 3 countries.
First and foremost, DON'T ride on busy streets! Geez, I Googled my ride and picked all side streets... a total of 250 meters of streets above 30 MPH. (50 KPH) Take the time to figure out how to ride your commute on side roads. Heck, in Florida there is almost no traffic on them.
Second, there is about a 200 meter stretch were I take the sidewalk, yep... never ran into a person walking on that portion of sidewalk at 6:15 AM in the dark.
Third, make it OBVIOUS that you are a bicycle! Screaming colors for shirts, reflective tape on the seat, reflective sidewall tires, reflective rack bags and panniers and multiple LED lighting. I use a Planet Bike 1/2 watt LED rear light that stays solidly lit. A flasher on the left side of the bike (indicates width) and an auto-leveling flasher on my helmet (indicates height) A single flasher is hard to focus on to figure distance away...but two of them will. My third light is solidly lit to aid the older folks on the road to let them know I'm there. Oh yeah, a HELMET mounted light is great since the movement announces you and you can look at drivers. Aim a L1D CE at a driver from 30 meters and watch them wake up. A L2D RB100 on the frame aids in lighting to see (two equals one and one equals none) People tell me I am easy to spot up to 800 meters away. Since I ride a recumbent, I look like a rolling freak show... 5 lights and reflective everything announcing my shape to the world.
If you are stuck in rush hour slow speed stop-and-go traffic, take the lane! If you can pedal as fast as traffic is going... move to the slight left hand side of the lane and take the entire lane. Once traffic speeds up, shift to the right but if it is slow. Take the lane so cars won't turn into you since they are not used to bicycles on the right. They won't rear end you, those 3 red LED lights and reflective everything are easy to see. The car in front of you has the brake lights so it works.
Use good tires! Since I ride across glass, rocks, sand, road trash and potholes, my tires are wider, kevlar belted and have a very thick tread to handle thumbtacks (Schwalbe Marathon Plus) I can ride through road construction, water, potholes and through grass/gravel without any problems. My front is 47mm (1.75 inches) wide with the rear 32mm (1.25 inches) wide. I deal with sand so I went wider than my normal 40mm (1.5 inches) The ground is soft here and the front floats better across grass.
Use a rear view mirror on your helmet. A quick glance and slight movement of your head allows you to view everything behind you. Some people think it looks weird but fashion is contrary to common sense and survival. Funny how mirrors are considered stupid on a bicycle but vital on every other form of transportation.
For signaling a turn, I do it "California style" I point with my right arm when turning right, point with my left arm turning left. It makes sense, it is obvious what I am doing and since I am not in a car... the signal can be seen from behind no matter the hand.
If commuting, get a bicycle that has front suspension. Not only is it more comfortable, it will keep the critical front steering wheel on the street and not jump around when hitting potholes etc. The rear is not as critical although my recumbent is fully suspended. Even chopper motorcycles have front suspension.
Put a BIG visor on your helmet. It will keep the sun out of your eyes, the rain off your glasses and will protect the helmet mirror. An added bonus is it creates the illusion your L1D CE is impossibly small. The flood coming off the light will light up the visor to aid in visibility.
Practice emergency stops with the front brake. I cheat with a recumbent which is almost impossible to flip although I have stood it straight up on it's nose. This only happens at the end of the stop so no worries. Spend the bucks on good front brakes and use them! 99% of my stops are front brake only.
The last thing to remember is... if your mother was driving behind you... would she be happy with your riding style or horrified? Keep safe out there, don't **** off other drivers and be predictable while being seen in the dark.
Rant mode off