a few tips for you:
1- keep scanning. Keep scanning until your aircraft is parked. Don’t allow any lapses in your scan.
Even if you are not in control of the plane. co-pilots or passenger should always help in scanning.
2- Keep the aircraft windshield clean. A bug-corpse nearby looks like traffic far away.
3- Eat a lot of carrots and don’t smoke.
4- Divide the sky into chunks about ten degrees across, so that there is no point more than five degrees off center, then check each chunk individually and scan along the horizon upright and down from the horizon too. Traffic at your altitude will look to be at the level of the horizon. Traffic that is climbing or descending toward your flight altitude will be within a few degrees off of the horizon. The FAA recommends that you dwell on each chunk for at least one second. That's a bit long, but avoid a steady sweep of the horizon line. What I mean by that is that you don't go smoothly from left to right, you take your time at about every 10 degrees but not to much time.
5- be careful of the empty-field myopia. Before scanning the horizon from looking at your instruments, look at your wing tip to aid your eyes to refocus to distant sight.
6- silly but effective, practice scanning when you're in a car
