I'm basically a beginner myself but I thought I could help as I've just went through a pretty crazy change in lifestyle on and off the bicycle. Here's how I started:

I'd recommend setting up a structured cycling routine and sticking to it.

Weeks 1-2:

Ride for 1 hour 3-4 times a week for 2 weeks at a comfortable but not overly easy pace. This will give you lots of perimeters to work with. You can increase the duration, amount of rides, or the pace in the following 2 weeks depending on how the first 2 weeks went. The goal is to not crush your will to live by over doing it.

Weeks 3-4:

Increase or maintain the amount of rides per week. Try increasing the intensity on a couple of rides during the week to see how that feels.

Weeks 5-6:

Try to ride 4-5 times a week with 2-3 moderate to difficult rides peppered in there. If you're planning for a difficult ride day bring some snacks to eat while on the bike. I was a bonking machine for my first couple months because I never brought food. IT SUCKS. Bring food.

I should also mention that as your fitness increases you will want to ride more often and harder. Time off the bike is as important as time on it. Don't over do it and listen to your body. If it was supposed to be a hard day but your legs and body are wrecked then just go out and put in easy miles. Don't beat yourself up over it.

Also, it's easy to get stuck in the rut of riding what you know. Try tweaking and exploring new routes while out on your rides. Changing it up is always a nice reminder of why bicycles are so much fun.

You can basically take it from there. I hope this was helpful.

Have fun and embrace the suck.