Time on the bike is how you improve both your endurance and speed.

There are many threads here on training schedules and programmes and it is probably worth doing a search on words like training, programmes, racing, and such...

Before we can give much advice, we really need to know what your goals are.

For example, my over-arching goal is increasing fitness with my cycling goals revolving around racing at club level with particular emphasis on time trialling. So if that was an interest for you, I would direct you to a thread in the "Tips and Tricks" forum called "Training for Time Trials".

If your goal is to ride enduro events like 100milers or more, then I would not have much in the way of specific tips for you.

If your goal was to commute to work, I could give you some ideas on what works for me.

So let us know your what your cycling plans are and we can maybe give you some relevant ideas for what you intend.