It's easy to get into a habit of permanently driving in a stressed manner; always pushing to make what feels like 'progress'. It's very possible to drive only a couple of MPH over the limit with constant throttle input, slightly too quick for the conditions and your whole drive suffers because you're rushing into hazards, constantly braking lightly (nose to tail traffic on the motorway, anyone?), and then pushing forwards again. You don't realise it because it becomes normal, and it's how most people actually drive, but you are stressing yourself out and your driving suffers.
I found a course of advanced driving worked wonders. My instructor is a police class 1 driver and also a retired police driving examiner and instructor. The things you learn!! I now find that I make way more progress. To a passenger, you seem to be driving slowly and calmly but in fact because you're throwing your awareness far down the road and
constantly planning your drive you end up making much more real-world progress. You barely need to use brakes, tend to use lower gears for flexibility, and you become much more harmonised with the forces, weight distribution and physics of the car and road. Also, you're aware of hazards developing before everyone else has even noticed the hazard you processed
five hazards ago while formulating your driving plan, so you are always getting ahead of the pack.
Before I took AD I was driving about 5mph to 10mph over most speed limits, subconsciously engaging in the traffic light GP, and always arrived subconsciously on edge after a tiring drive. Post AD course I find I never break red-ring limits and make full advantage of de-restricted roads, and it's so smooth and calm I can drive for eight hours without feeling tired. I get to places faster, am getting around 5mpg better fuel economy, and everyone seems to enjoy the drive more.
Everyone thinks they're an above average driver, and statistically around half of them are wrong!

You'd be amazed how much 99% of the population need to learn but don't. You can spend weeks just learning to change gear properly (seriously!), or how to brake really smoothly, or positioning for maximum safety, view and progress. It's massively engaging, really enjoyable and you'll naturally slow down.
When you realise just how much there is to take on board when you're genuinely paying attention and analysing hazards (especially around urban environments), you genuinely can't help but slow down. It's automatic, because your brain works so hard processing all the developing hazards and formulating your ever-changing driving plan that the speed just melts off until you consciously decide you need it (change of limit, overtaking, pressing on where suitable etc).
"Thirty MPH limit and I'm doing 30. Pedestrians ahead, mirror, position of safety straddling the central white lines. Off the gas, junction ahead, road markings indicate hazard ahead. Road sign confirms the hazard, mirror, taking a nearside position to negotiate the upcoming offside bend, back on the gas hard now..."
It's impossible to process hazards properly like this and speed around like a loon in a daydream. The latter is exactly how 99% of drivers carry out their journeys. They pass their test, then slowly relax into a zombie-like state of only analysing the major hazards (the car in front, someone stepping out) and their safety bubble only extends six feet in front of the car. In AD you should be analysing hazards right to the horizon and back again, and trust me it's very mentally engaging.
With a few week's practice under qualified tuition you'll find your speed melts away, you're much more relaxed and soon lose the 'traffic light Grand Prix' mentality because you come to understand that letting other motorists get out of your way to have their accidents elsewhere (far away from you) is the best way to keep yourself moving and away from things that will impact your drive and your passengers.
Buy a copy of
Roadcraft, and I also very highly recommend
this book by an ex-police instructor. You don't need a Kindle for the latter, you can read it in your browser. Then sign up with the IAM, RoADA or a suitable ex-police instructor in your area and have an assessment drive. You'll be amazed at the things you didn't know you didn't know!