I would say that 90% of the players strength comes from how good one can correctly "read" a number of moves forward. A good way to practice this skill is to play many games of go but it's even better is to solve lots of go problems. As a beginner, you can barely manage to read one move ahead, but with a little practice, you can soon read ahead 2-3 moves correctly and with a lot of practice 10 moves or more.

When you have solved a problem, you should be so sure that it is the right solution so that you do not need to look at the correct answer. Therefore some problem books are lacking a section with solutions. So you have to have read out the entire problem with all possible variations before deciding to look at the answer. Sometimes you are still wrong and then it is important to try to understand why it was wrong and why the correct answer is right.

You do not have to spend hours on end to solve problems, but it is perfectly OK to solve one problem here and one there. Eg when sitting in the subway, before going to sleep, sitting on the toilet, waiting in line, when there are commercials on TV, etc. So buy / borrow some problems books, spread them out in your home and always have one with you wherever you go. ;)

On the internet, there are some problems collections to come by and the best is undoubtedly goproblems.com. There you can easily start with the problem that suits your personal level and then advance. There are currently 8035 problems, of which I've made three.

There are also some "apps" for smart phones (Android / iOS), which has many go problems. I have yet to find any that is easy to use and that I think is good for beginners, but I have not been looking so hard. Those that cost money are probably also the ones that are best. Please tell me if you find a good app.