My DH words of wisdom: "Only do it if you're capable of catching them"
. DH and I had to catch the little ratbags tonight (DD usually folds herself into the run- those gymnastic classes weren't wasted - ) I had to catch the girls in their HopInn tunnel and our boar by coralling him into a corner.
Even though it was getting dark and they wanted supper, they saw the chance to muck about
First off - secure run, don't take chances with their safety. We peg ours down with those heavy duty tent pegs. I put cable ties on the doors to fasten in case something tries to pull at them.
A box or something to hide in, security and shade.
Check the grass is dry - walk barefoot on it.
Put a folded newspaper down if they want to sit on it.
Daisies, buttercup, anything like ivy, bulbs, dock leaves. Look out for spikey weeds .there's ones like dandelions but really prickly. Ours leave anything like buttercup (by instinct I suppose) thankfully.
Give them maybe 30 minutes to begin with, build it up slowly.
I give cut grass in the days before they can graze to get them used to it, they love it 
You might be rewarded by a few mad popcorning circuits (take your phone to video them, its so cute )
When its really hot, a sheet over the run to give shade .
A water bottle
Ours like going out in the evening when we get home from work (or DD from school)
And you'll need to move the run when they've done their locust impression, but you'll be left with tiny packages of fertiliser !