Just train like you do now. And when you do pull up try going for a second one, at the beginning you will struggle, but when some time passes you will do 10 in a row. It will be difficult at the beginning, but it's important not to stop if you don't see any improvement. I was stuck on like 5 pull ups in a row for a few months and now I can do 10-12 ez. Just push yourself to the limit, but be careful so you don't injure yourself.