Join a cycling club (and yes, you will be slower)

Joining a cycling club is something every beginner cyclist should do. Club rides make cycling safer (safety in numbers) but also massively help your own learning curve as a cyclist (they'll show you the ropes in terms of group etiquette, basic bike maintenance & repairs, how to ride safely on the road and you'll also have someone to ask those questions you have as a newbie, like do I wear undies under my lycra). Most decent clubs run a beginners ride once a week or month. Go. You'll also probably meet some nice people who live & ride in your area, so you'll also get the tips on good places to ride (and avoid), best routes to commute, best local coffee, etc, as well as make some new friends. And if something bad does happen on a ride, you'll be riding with people equipped and prepared for such situations.

Too many beginners fall into the thinking "I might slow them down", which is a shame as they will benefit the most from the experience around them on a club ride. And yes, you probably will be slow to start. Guess what though? People don't care. The people from the club leading the ride (who are quite probably very experienced and fit) don't lead a beginner's ride with the expectation they can blast along at their normal speed. Quite the contrary. Beginners rides are riddled with mechanical issues and have a slow average speed. Why? Because the cyclists are beginners. And that's true of everyone on a beginner's ride - they know what to expect.

And clubs have members of all standards. Ranging from uber-fit, shaved leg 20 somethings through to more gentler paced octogenarians.

So will you be slow? Probably. But that's expected.

If the people leading the ride want a good physical workout they'll do other rides. If they are anything like the people why typically lead rides in my club (the Dulwich Hill Bicycle Club) they are very strong riders who rack up 10000km+ per year. Even with 12 months hardcore practice, you'll still be "slowing them down". But they don't mind leading some beginners, as it will see their club grow and they love sharing their sport with others.