Do you live in a city where acting courses are readily available?
If you tell us where, many people can no doubt recommend classes.
Otherwise, you can work both alone and with friends. Alone, you can get plays from the library, read them, choose a character (it doesn't even have to be an appropriate character for your type) and start thinking about who they are (class, age, gender, background, etc.) and what they want in the play and what they want from the people they interact with in each scene. Think about what they expect before they come into the scene, and how what happens in the scene affects that expectation. Try reading their lines out loud, partially simply to get used to saying lines, and then to start thinking about what they are trying to DO with each line. Rephrase each line in your own words. Etc.
You can also get books of monologues (or find free ones on the Web - my site has some), choose one, and develop a back story for the character, a clear idea of where they are and when, and then what they want from they are saying. Imagine you are speaking their words to very different people - a family member, a teacher, a person in a shop, etc.
You can also see if some of your friends are willing to just read through plays with you, and then discuss the kind of questions I outline above with them, and try working the ideas you come up with into how you read the lines.
Etc. There are whole books on this kind of thing. The best solution is to find a class and start failing enough to succeed in a meaningful way.
Either way, have fun. Even in the sad stuff. Explore your inner self, your understanding of the world, the author's words. Do whatever you can to feel larger through the work.
For what that's worth..