Finger stretchers and warm-ups.

Here are some ways to prepare yourself for practice or performance.

•  Warming up: Some simple exercises to warm up should be the first thing you think of when you're preparing to practice or or perform. Playing some chords, picking out notes or scales, and stretching exercises are all important. If you play fingerstyle guitar, doing some right hand arpeggios is also necessary.
• How to stretch your left hand. Doing stretching exercises helps to strengthen fingers as well as gain independence. Too many beginning guitar students avoid using the pinky. While it's possible to play without it, there are good reasons to use it. Start out by playing the 1st string, 1st fret with your index or 1st finger. Without taking that finger off, play the 2nd fret, 2nd finger, 3rd fret, 3rd finger, then 4th fret, 4th finger. Reverse the fingering, 4th, 3rd, 2nd, 1st and do that at least twice on each string. The key is to not take the 1st finger off during the whole sequence. The exercise will become increasingly harder as you get to the thicker strings. Be careful not to try to do too much at first. If you're in pain, stop. Once you can do that, try using different finger combinations to help improve dexterity. Ultimately, all 4 fingers should work equally well.
• Right hand exercises. Fingerpicking players should play different arpeggio patterns while gradually increasing speed. Getting a steady thumb beat going, followed by smooth picking with the fingers will sound good. A simple arpeggio pattern: Thumb, Index, Thumb, Middle. The thumb alternates bass notes, the index plays the 2nd string and the middle finger plays the 1st string. Once you get a solid bass line going, add the other fingers and try to play a slow, steady rhythm.
• Isolate trouble spots. When preparing a song for performance, spend extra time on troublesome passages. Work through them slowly, paying particular attention to using the correct fingering, playing the right notes, and then tightening up the rhythm with a metronome. Don't practice a song too long without listening to it. 

These techniques will help you improve your playing, warm up properly, and build the confidence to perform songs under pressure.