Here is a good warm-up exercise shown to me by Pepe Romero that can work on many technical aspects:
Figure 1 works on synchronizing your left and right hand, speed, and right hand finger alternation. Once you get the pattern down, move up the neck of the guitar on the same string continuing the pattern. I usually go up until my pinky hits the twelfth fret. I then move down the neck using the pattern in Figure 2.
Notice the slurs. I try to pick up the pace as I fall down the neck, using the slurs to help bring up the tempo.
Start these exercises slowly. Then, once you have the pattern down in your fingers, you can bring slowly bring up the tempo. For example you can start out playing quarter notes, then, during the next cycle, eighth-notes, etc. Play Figures 1 and 2 on all 6 strings of the guitar.
Slight right hand variations can work on different techniques. For example alternating between m and a in the right hand to strengthen those weaker fingers or playing them with rest stroke and then playing them with free stroke.
Enjoy!