There's nothing wrong with reading mainly one-two genres and many do so successfully, although it may lead to reading burnout. Talking from my own personal experience - I used to read a lot of crime and thriller books, but now just the thought of reading another book of these two genres gives me shivers.

As someone who discovered new genres in the last years, I found helpful:

• Reading lighter or shorter novels first. For example, in case of sci-fi, those books were The Hitchicker's Guide to the Galaxy and Do Androids Dream of Electric Sheep. Both of those demonstrated that sci-fi isn't what I thought it would be.

• Trying out subgenres or books with multiple genres combined. For example, I like some aspects of magic but high fantasy with complex magical systems is too much. So instead I read urban fantasy, magical realism and fairytales.

• Choosing based on some elements from books you have enjoyed. Environment, atmosphere, era, characters, etc. For example, I love Sherlock Holmes. So when I learned about Agent Pendergast series, I had to give it a try even though horror isn't exactly my cup of tea. Needless to say, I enjoyed it a lot. Another example is my favorite urban fantasy series, The Rivers of London, that not only takes place in one of my favorite cities but also combines police work with magic. I mean..it's perfect combo in my eyes lol!

So to sum up, only thing that helps is to choose books more thoughtfully and read, read, read. It takes time and experience to learn to put aside your biases and expectations and to appreciate different genres and what they can offer imho.

Edit: wording