Me personally? When I set up a new tank to add to my existing four?
I either:
A.) Wait until either Travis or I clean out a filter and steal Eheim cocoa puffs and stuff them in an old pair of nylons. Add to new filter with a stinky sponge or some stinky floss media from one of the running filters on one of our combined total of 6 tanks between our two houses, stuff them into the new filter, and jam on. 24 hours later, I start stocking my tank.
2.) If I can't beg Travis to clean out one of his monsters (he calls them his sons, they are actually industrial sized eheims or something like that, I don't know, all I know is I am jealous because I want one) because cleaning them out is a pain, and I have already raided all my own media for usable seeded stuffs, I set up my new tank, and seed the substrate layer with sand from my tanganyikan tank like I am making a lasagna. Then I sneak over to Travis's when he isn't looking and steal plants. I use them to seed also.
III.) If I have time, I'll seed rocks or media in either my tang tank or Travis's tank.
Quatro.) When I am feeling very organized, industrious and keen, I run an extra, old HOB stocked with just ceramic noodles and eheim cocoa puffs just for seeding for new tanks. I use that media and start my new filters off with that. I generally will run that on my tang tank, since it is currently the largest I have (I am hoping to change that....REAL soon [there is a 125 on the horizon...be afraid. Be very afraid. I smell either a S.A. planted or possibly A .....REEF coming on]).
Now, all this said, I tend to keep some worker fish on hand. Danios. Yes, I am a preacher of giving all fish equal treatment, and treating all fish as pets with respect, etc, etc. However, I also believe in breeding your own feeders, feeding live feeders, etc. Therefore I feel justified in keeping worker fish. They are well cared for while they work, and are never disposed of. Yes, they sometimes die in their duty. However they are not mistreated. They serve as cyclers during the times I am starting a tank (for about 3 days) then lived usually in the tang tank as dither/toys/entertainment for the cichlids. I do not endorse the 24 hour stock for everyone. I do it because I have no patience, and because I am confident enough to be dumb. So far, I haven't had any trouble. But I am telling the truth about my experiences.
I guess my disclaimer is: While I am more cavalier, it is better for most to be more cautious