To add to everyone's good advice...
My golden barrel is about 12 inches wide (the body, not counting spines) and it hasn't even thought about flowering yet. No fuzz at all. I am definitely not mistreating it so I think it just takes a long time for them to flower. The Ferocacti tend to wait a while too. Our native Mammillarias flower several years sooner than the native Ferocacti.
I had the second plant (the Austrocylindropuntia subulata crest) for years and it never flowered. I think AgaveGirl recently had some flowers on her non-crested plant, so this is in theory what they would look like if they ever ventured forth.
https://garden.org/thread/view...
As for the general question in the title, I would be most curious about people's strategies or voodoo magic for getting great cactus flowers. I would imagine strong light is probably really important (I consider it mandatory for my own plants). Some cacti are real shy to flower here (they get part of the way or the flower never really opens up) and I think that's because our climate is too mild and doesn't provide the kind of heat they need to really pop. It's like they're waiting for something that never happens.
My own experience (providing regular water, when the soil goes dry, but not leaving the soil dry for days and days on end) is that the actual fertilizer you use is not that important, if it's a reasonably balanced formula. The quantity you use is much more important, or easier to get wrong anyway. For reference I use 0.5 tsp of liquid 7-9-5 formula per 5 liter bottle. (Metric and gringo units commingle here as you would naturally expect.)
You can scale accordingly, based on the the first number in the N-P-K listing. 5 liters is about a gallon, if you want to round to the nearest container. My dosage works out to be a little under 50 ppm N, and here is a handy calculator to arrive at that precise amount with your own preferred brand.
http://firstrays.com/free-info...
Now your fertilizer will come with dosage recommendations and they are generally way too high for succulents, especially out of the blazing sun. The Miracle Gro granular product was recommended at 20 times the amount I use. Try a quarter or less for starters, or use the handy calculator to arrive at a sane dosage. And don't fertilize every time you water unless you are prepared to flush the container well every time.