if you have to ride brakeless (when you say by default, i'm assuming you're getting a brakeless bike and have no money/parts for a brake. same way i started sans brakes), then...well...you just kind of have to do it. keep yor eyes open. pay attention to your peripheral vision, use your ears like they're eyes in the back of your head. look through car windows to see drivers inside getting out, or when you're in traffic to see other cars and what they're doing. use other cars and some buildings and storefronts as mirrors to see places you can't see. if it rains, use the streets to look for the headlights of cars as they come around corners.

at first i took it slow and learned what to watch for, and spent a lot of time in a park at night, skipping, skidding, trackstanding, doing tight, slow circles, all the stuff you do just to practice control of the bike. work on control first, speed second. you can rock a brakeless bike damn fast, i know i do. but when you're just getting used to it...speed can get you hurt if you don't know how to counteract it.