I have to 2nd what OlveraUK wrote. i'll play a scale I want to learn very slow until the muscle memory kicks in. Muscle memory is when you can play something without thinking about it. For instance-if you asked me to play a C chord I can do it without looking at the fretboard. My fingers can do it easily because I've done it thousands of times. So I practice a lick slowly over and over until I can do it easily and then I'll practice how fast I want to do it. But as Olvera said, I might not be able to attain the speed I want because my fingers won't go that fast accurately. Eric Clapton is also known as "slowhand". He can play a slow blues scale with such depth and feeling that it is very hard to reproduce. You don't have to play at the speed of light to be good!
Something that is not talked about that much is taking a day off from playing. If you ask someone who lifts weights and is in to bodybuilding they will tell you not to lift every day. Taking a day off allows your muscles to heal. Recently I've playing with a rockabilly band(think Stray Cats) and since I'm not familiar with that style, I've had to practice a lot. My hand was so sore I couldn't do a barre chord. So I took a day off and my hand is back to normal. As you play you'll find your limits and what you need to do to overcome them. Good luck and have fun-John