[Johnny Footstool]

I've been playing since high school -- more than 20 years now.

If you are frustrated and want to improve faster, definitely start taking lessons. I learned from books and it took forever. It was a year before I could sit down and play an entire, somewhat-complex song in front of people ("More Than Words" by Extreme was big at the time). I wasted a lot of time trying to be self-taught, and I missed so much. I'd be a much better player now if I had taken lessons in the beginning.

Do you have friends who play? I really started improving after I began playing along with other people.

Starting on an acoustic is best; it helps you build strength and learn the proper form.

One of the best ways to motivate yourself is to pick a song you know and love and learn how to play it, or at least a version of it. Hopefully, you can find guitar tablature and instructional videos that make it easier.
-Learn which chords are used in the song, and practice those. Practice switching between them.
-Learn one part of the song at at time -- the intro, the verse, the chorus, the bridge.
-Practice every day, for 15-20 minutes only.
-Don't try to play anywhere near full speed for a while -- you'll only get frustrated.
-Take it slow and steady, with the goal of being able to play a recognizable version of the song in a months' time.