Just build it up slowly, increase your distance, mainly enjoy it. Set yourself realistic goals, then you will smash them, which will definitely help your mindset. I started last July, my aim being to cycle to work (16 miles each way) by spring- I did that October, my main goal was to cycle 60 miles for a sportive this August- which is now September and 100 miles. I have built up my distance gradually, got over the 30 mile mark, reached the 40, then 50. By doing that I have built up my stamina, which has built up my fitness and speed.
I absolutely love it, and if I can cycle anywhere rather than drive I will. I have found I have a determined, stubborn and rather competitive streak too.
Majority of my rides are solo, but when we can, me and the husband go out. He never pushes me, but I always find I go faster and further with him. My 50 mile was my first group ride, and that was even more of a push, with other people about, and so much fun.
I always use strava,mainly to clock my distance, but it makes me feel good if I can improve on certain stretches.
I have also found, that now I am fitter, I can go longer stretches of not actually stopping pedalling, which makes me faster.
But, we are all different, so just enjoy it, that is the most important bit!!