Healthy broodstock produces healthy eggs and larvae.
As I've mentiond before, your broodstock pairs need a healthy and varied diet to produce viable eggs. They also need to be fed often. I feed my pairs four times per day, every four hours. This is known as conditioning.
Please read through the page of food recipies that I use. If you keep your fish well fed you will be well on your way to getting them to spawn.
There is no set time for pairs to be together before they start to spawn. It could be a few weeks, months or possibly never if they aren't a compatable. The easiest way is to start with a pair that has already bonded and spawned for someone else. This is the more expensive way to go but, if you can get a pair that is already spawning chances are that they will spawn for you sooner than a newly matched pair.
In a pair of clownfish, the larger one will be the female. If you are trying to make up your own pair the best way to do it is to get two fish that are of different sizes. Not a huge difference in size but an obvious one.
The Happy Couple
After the pair has been together for a while they should, hopefully, form a pair. If you are keeping the pair in an isolated tank with only a clay pot or ceramic tiles and feeding them often, there isn't much else to do than produce babies.
Here is a video of my pair of "Darwin" A. ocellaris during a spawning event:
This pair was sold to me as a mixed pair, A. percula and A. ocellaris. After careful observation I'm pretty sure that they were both A. ocellaris:
I no longer have this pair.
Clownfish will spawn in a variety of places. In a reef tank they will often lay the eggs on a partially hidden area of rockwork, cave or on the glass. For breeding purposes a breeding pair is usually kept in a bare tank with a clay pot (as seen above) or ceramic tiles.
When I first started out I used the clay pots but have since switched over to tiles. Eggs laid on clay pots can be difficult to aerate since you're trying to get the bubbles to flow around a curved surface. Tiles are much easier since the eggs are all on the same plane.
I use three tiles for each tank. One on the bottom, one against the side of the tank and one on a 45° angle that creates a lean-to configuration. A suction cup and clip from a heater stuck to the bottom keeps the tiles from sliding.