Here are a few tips to decrease the risks of injury.
As a beginner, prefer problems that are less than 3 or 4 meters high and with a good landing (even ground, with no rocks/roots/etc)
It can be reassuring to have several boulder pads to cover a larger surface on the ground.
If you climb with a group, you can also ask your friends to move the boulder pad while you're climbing, so that it always stays right below you.
To help your friends climb safely, you can offer to be the spotter.
The spotter redirects the climber's fall to land safely on the boulder pad.
Careful: don't try to catch the climber yourself, you might injure yourself! The goal of spotting is to help the climber land safely. This might be stopping their head from hitting the floor, or, directing them in the air to land on the mat.
It can sometimes be tricky to go down from a boulder once you're on top. Check the descent beforehand — especially if you're alone!
Dartmoor's granite has very large and sharp cystals.
It is often better to stop the session early before you start to bleed. It is quite normal for your skin to give up before your muscles.