Some things that have helped me over a decade of bike-only lifestyle:
- Sightline - maximize it to see and avoid that dead animal, pothole, tree branch, tire scrap, easy chair (seriously Kansas City what the fuck). When riding behind a car, your bike should be aligned with a side mirror so they can see you and you can see past them. Don't dwell behind trucks, buses, or anything carrying a load. If you're stuck behind one, give yourself a buffer for blowouts or obscured hazards.
- Pace - In general it's best to be slightly faster than the average on highways. Even if you are overtaking a lot of other vehicles, you should still push towards the slow lane whenever possible. Getting passed on the right (or left if you're in a left-hand country) is generally bad form and hints at a lack of awareness. If you want to cruise at an easy pace, find two cars in the slow lane with space between them and slot in, but don't be the rearmost slow vehicle in a line.
- Second mirror check after head check - Most riders do a mirror-check, head-check, and go. Instead, after your head-check, give your mirror a quick second glance. Consider if a high schooler in his parents' Mustang GT just crested the hill 1/8mi behind you at 110mph. He'd be approaching your ass end at 60mph and hasn't yet spotted your tiny brake running light. Do you think he can slow in time once he does? This idiot is rare, but look out for him whenever the left lane opens up. This doesn't just apply to actual lanes of traffic, it is a relatively normal on the DC Baltimore-Washington parkway and Massachusetts turnpike to see people passing on the shoulders and exit lanes, so be on the lookout.
- Fail your assumptions - There's a semi or city bus you intend to pass. Is there stopped traffic, a disabled vehicle or debris in the lane adjacent to and obstructed by it? Do your checks for each lane every time, NEVER swoop across multiple lanes at one, that is an easy way to die and not worth the half second you save. Take the next exit if you have to.
- Don't ride at all on drinking holidays. The closest call I ever had was riding home on a rainy new year's eve, some guy in a pickup truck blew a stop sign and made a left-hander in front of me. Because it was dark out, I didn't notice he failed to stop until I was maybe 15 feet from his front grille, and I swerved into the opposing lane to avoid a head on collision. I am still astounded that he didn't hit the rear end of my bike, it was a flash.
- Don't get complacent. Risk management is a constant process, you should be scanning for hazards, doing "what-ifs" and adjusting proactively. If you find yourself fixating on something for more than a moment, force your gaze away from it and rescan the whole picture. If something surprises you, take the time to figure out why.
- Evaluate your habits while you're off the bike. We live and die by them, so if we reflect on them honestly and make the effort, we can improve.