If you want hands-on (practical) experience then I can only advise you to do the OSCP course

If you don't feel ready for the course then I suggest some self-study and if you're into SQL Injection and similar (Web Application Security) then you should begin to learn a Dynamic Web Language such as PHP or ASP in order to understand the vulnerabilities even better if you don't already know these.
When you know this and of course HTML too, then it's easier to understand how the vulnerabilities work, why they exist, how to find them and how to patch them

That's just my recommendations though
