The easiest way to get experience on set is to work on a few student or independent films. These all have minimal budgets and ask for volunteers. You'll find casting notices for these kinds of films on facebook community pages and online casting sites.
Showreels are a must so that you can be considered for a role. These need to be short and sweet. If you have no idea what to put on your reel, have a look at my book Cool Stuff For kids To Perform, it's full of short scripts for kids of all ages.
Every credible actor has a resume which is kept constantly updated. List all your experience and any training or workshops you have done on your resume.
Workshops with casting directors are a great idea, as you get to meet the person who is casting actors and get an idea of what they are looking for. Remember every casting director has different ideas, so you need to adapt your auditions to suit the person casting you.
Have a look at my vlog as I talk about all these points in more detail on here.
Once you have compiled all this information you are ready for the next step and that is marketing yourself. Who do you send this information to? How do you approach producers, directors, film makers?
But that's a whole other blog, so stay tuned. :)