I have no idea what your experience is, so I'm just going to pretend you've been toying with the idea, but haven't acted upon it just yet.
If that is the case then
I would suggest you sign up for acting lessons so you can find out what it's like to act etc. and experience first hand what it'd be like for yourself.
Usually you'll get about 36-40 lessons, and during those lessons you act your way up to a final production (a play), some clubs organize two plays a year.
So not only will you be able to improve your skills/get criticism, you also get the chance to experience what it's like being on stage/actually acting. You could also ask your teacher about information on becoming an actor etc. and he/she could help you to improve further and give you information on where to audition/how to audition etc.
I think there's even lessons that focus on being filmed and how to come across when being filmed etc. (as it's obviously quite different from being on stage in front of a live audience). You should look into those as well if you can.
If that doesn't work out for you, I think improvisation would be great for you as you don't really need to learn your text word for word. You just have a 'red line' to work from (e.g. You're at the dentist, in the waiting room, and you're very nervous).
There are a lot of clubs (as in bar type of places) where they organize nights on which they have people play skits on stage, but also do improvisation games (e.g. a cluedo type game where a researcher interviews all the people of the house.. each person adds to the story of how the person disappeared (or didn't) etc.).
But if you take acting lessons, you'll learn how to improvise as well.
