It can be a real loss of your manhood when you have to explain to the wife how you got that bruise while beating a civilian, so learn a few important tips before you go out in the field:

1 Make sure when you are beating a civilian to have at least 8-10 well armed friends with you, preferably surround the target (as shown here)
2 Don't forget to protect yourself - I know, I know, putting on that helmet and riot shield can be a pain but you'll thank me later!
3 When the body goes limp, make sure to keep hitting it with a stick occasionally to show it who's boss

That's about it! Remember, you may feel a bit tired after a while, but with enough practice you'll have all the endurance you need.