Check your position on the road, i.e. that you are riding assertively and can see and be seen. Consider how positioning alters with different traffic/road situations. A training instructor riding behind can assess your position on the road and give you constructive feedback.
Consider how you communicate with other users of the road, from signalling to making eye contact with drivers behind. What works best? A smile does help..
Understand what should be considered when sharing the road with HGV lorries/bus drivers including a lorry’s blind spots and when turning left/traffic lights. Make a point of looking into the driver's mirror when overtaking.Do not undertake.
One-to-one training will help to iron out any issues you may have with more complicated traffic manoeuvres including positioning in multilanes and common problems such as positioning at junctions, taking corners too tightly etc.
Understand more fully legislation on all aspects of road cycling from lights to cycle boxes, including current cycling issues such as cycle superhighways and what you should do if you are involved in an incident.
An instructor can give your bike a quick check and also assess how your riding style might be improved. Often a small adjustments to your bike (moving saddle, changing brake lever positions etc) can make for a more comfortable ride.
There are a lot more cyclists out on the road. Consider your interactions with fellow cyclists as well as cycle lane etiquette. Be considerate to other less experienced riders... you were there once yourself. When cycling in shared space (parks, canals), pedestrians have priority.
Consider taking an urban cycling session, it will consolidate the stuff you do know and it may improve the way you ride on road.