To echo Yonan: Look, read, and watch. There's absolutely no substitute for experience, but establishing some groundwork is a major boon - not only will it help you avoid some of the pitfalls common to new painters (thin your paints, keep your brushes clean, etc.), it will also get you more accustomed to the core concepts and terminology painters use, which will help you better communicate issues and capitalize on advice received, as you and your painting progress.
That said, you
will need to practice. You can spend five minutes reading about some techniques and be well on your way to proficiency (washing, drybrushing, etc.), but things like brush control and a feel for paint consistency only come with time (granted, some need more than others

).
If you're able, posting pictures of your work also helps a great deal. There are lots of experienced painters on Dakka that can spot specific issues from a photo without even needing a prompt, but it's a lot harder to guess if your paint is too thick from a description (okay, bad example - if you have to ask, it probably is!).
In short: Read more, watch more, paint more. When you get stumped or stagnate, open it up to the community.