DON'T watch the game, watch the players. Watching to know when a mugger is coming is different to watching the action and not the players.
Pair up with your opposite, make eye contact occasionally and use hand signals if you see someone hit, think a player needs checking, or you believe the ref could move to cover the area better.
If a player changes sides of a barricade, you must be able to see them, so move if you have to.
If the game is being 'slow', I occasionally check a certain item on a player like all of the goggles/hoppers/packs.
As players move or get taken out, move off the tape onto the field if you aren't already there, be dynamic and always think about the best way to watch the players you need to watch (what angle? standing up or lying/kneeling?)
run-throughs or 1-on-1's, if you don't work in a team it's hard to know who shot who first, work together and if you didn't see what happened, don't make it up! Ask what your opposite saw or the next person up from you saw.
Don't automatically believe players who tell you it's bunker rub- look at the shape and whether it has shell in it (and whether the bunker has any paint of that colour on it!)
However if the person's been lying/kneeling on the ground don't be too harsh, might just be broken paint make an informed decision.
If you KNOW, really know you've seen a hit but it's been wiped or slid off by the time you get there, have faith in yourself and pull them. The hit doesn't have to still be there for them to be pulled, if you saw it, it goes.
The ultimate will
always support you, unless you're well out of order.
Watch for flinches, or suspicious movements (rubbing oneself sexually on a barricade isn't generally normal, but I have seen it
), swapping of hands for no reason, dropping to one knee might be because they have been shot on the knee.
Wear protection!
You have to get in there, and to be a good ref and to protect yourself you have to be able to take hits (and you will). Hat, neck protectors, chest protector and slide shorts are awesome.
Be willing to watch and learn, I've learned so much off a few certain people (thanks).