It doesn't matter what style of banjo playing you do, creating a warmup routine for yourself each time you pick up your banjo will help you progress and perform better. Playing the banjo requires some very specialized technique in your hands. If you try to come right out of the gate and play full speed, your playing is most likely going to be sloppy.
Professional athletes have a very specific warm up routine designed to help them perform at their highest levels. The same can be said for musicians. In order to play your best each time you pick up your banjo you should develop a specific routine. Without this, your playing can be filled with mistakes you otherwise would not have made and you can become frustrated and have less desire to play in the future.
I like to take it down to the absolute ground level when warming up. I first start with focusing on just my right hand (assuming you're right handed). I play everything VERY SLOWLY.
3 Finger Style 5 String Banjo Warm Up Excercises
If I am playing 3 finger style 5 string banjo I might start by simply doing a thumb and then a pinch of the outside strings.
I focus on making sure everything is hit as cleanly as possible before moving on. I might then take one simple roll such as an alternating roll and slowly go through it. Again, making sure I am striking the strings cleanly and accurately. Next I might do a forward roll on one string at a time making sure I have it cleanly on one string before moving on to the next string.
Another great 3 finger warm up excercise that brings both the right and left hand together and is great for your single string technique is to do the following pattern all the way up the neck and on every string. The tab only shows it being played on the 4th string up through the 7th fret, but follow the pattern and make sure you go all the way up the neck and on every string.
The pattern is just a forward roll, but starting first with an index finger.
Clawhammer 5 String Banjo Warm Up Excercises
If I am playing clawhammer banjo, I would probably start with a very slow basic bump-ditty clawhammer pattern. I then would start some very slow drop thumb patterns.
Tenor, Plectrum, 6-String Banjo Warm Up Exercises
For banjos that you play with a flatpick, you can use the same basic concept for warming up. I would slowly focus on down/up picking of one string and match it up with your left hand fretting. This exercise is similar to the last exercise shown above for the 3 finger style. Again, go very slowly and make sure you are playing every note very cleanly. The tab below just shows the 1st string being played up to the 6th fret, but make sure you go all the way up the neck following the pattern used below. Do this on every string.
The main thing is that you develop a warm up routine for you. These exercises are just a few examples of what to do. There are many more possibilities. Just make sure to go very slowly and focus on playing every note cleanly. If you can't play it cleanly, then go slower.
Let us know in the comments below some of your warm up routines!