Breeding the crested gecko in captivity can be a very rewarding experience.  Although slight changes in temperature can be helpful, Crested geckos do not need to be cooled or require any kind of temperature cycled to breed successfully. 

Males

Once males reach 4-8 months of age, a hemipenile bulge will develop at the base of their tails.  They become sexually mature at about 6 months of age, but they're usually a little small to be put in with a big female at that age.  I generally wait until they weigh 20-25 before I consider putting them in with a female.  

Don't forget that outstanding males are always more valuable to a breeder because his genes can be passed on to literally 10 times more offspring.  In other words, choose your males wisely.

Females

Once the female is about a year old and in the 30-35 gram range, a male can be introduced to her enclosure.  A big/fat female is not always a healthy, productive breeder, so take it easy on the baby food if you're trying to fatten a female up in order to make breed her sooner. 

The hatch rate of eggs from first year breeder females is generally lower than is the case with eggs produced by older females.  Don't get discouraged if you get some bad eggs from a first time breeder.  A healthy, mature (2+ years old) female will generally lay a clutch of two eggs every 25-40 days.  They will breed year round, but most females tend to "shut down" after 7-9 clutches.  It's a good idea to take the male out and let your females rest for 2-3 months a year.

Putting Together a Breeding Group

I generally keep three or four females per enclosure and then move males in and out for breeding when necessary.  You can easily breed one male to 3-4 groups of females throughout the course of a year.  When the males are not breeding, they're kept by themselves in smaller enclosures, but there's nothing wrong with leaving them with different groups of females year-round.  Larger females can become territorial and bully their younger, smaller cagemates. Although they generally seem to pick on other females, young males can also catch a beating from time to time.  Be mindful of this when adding young geckos to a group and if the agression looks to be getting out of hand, separate the geckos and try cleaning the cage.  Sometimes getting rid of all the scents in the cage can help make it feel like somewhat of a new home for everyone, including geckos who were already residing in the age.

The Nest Box

You won't see fertile eggs for at least a couple months after the geckos are introduced, but provide a nest box anyway.  This way, the female will become comfortable with it.   After 60 days or so, it's good to get into the habit of checking for eggs.  I check for eggs almost every day due to the number of females kept in each enclosure.  If you only have one female, you don't need to start checking for eggs until about 25 days after the last clutch was laid.

If you use any type of heating, the nest box should be placed on the coolest end of the cage.  For a nest box, I use a 4-6 quart container with a 2-3" layer of substrate.  The substrate I use is a mixture of 40% coconut fiber, 40% peat and 10%  play sand.  This mixture packs well, absorbs and holds moisture well and is safe for the eggs.  This mixture is just something that kind of evolved here over the last several years, but it seems to work better than anything else I've tried.  I do leave the lid off of the container, but I place a hide box on top of the substrate.  This gives both the males and females a cool, humid retreat.  It should also be noted that females regularly make use of the hide box when laying their eggs.

Eggs & Incubation

Temperature
Eggs should be kept at room temperature.  The cooler they're kept, the longer it takes to hatch...conversely, the warmer they're kept, the faster they'll hatch.  Although the idea of having eggs hatch faster sounds good, hatchlings that hatch earlier tend to be smaller and sometimes even weaker than normal.  The general rule of thumb is that longer an egg incubates, the larger/stronger the hatchling.   That said, it's probably best to keep eggs in the mid 70's, although fluctuating temperatures are OK too. 

Incubation Period
Depending on the temperature in the room, eggs usually hatch after 60-90 days, with the average being about 70-75 days.  In the winter, when temperatures are cooler, eggs can take as long as 120 days to hatch. 

Incubation Medium
I used to do perlite at 1:1 perlite to water by weight, I recently started doing 1:2 (perlite:water) and we rarely have to add water.  The trick is to make sure the perlite is relatively deep in comparison to the diameter of the container.  Some breeders mix it a bit on the drier side with good results too.  I use 6.75" round deli cups, which are about 3" deep.  I put in pproximately 2.5" of dampened perlite.   I like to have just a few ventilation holes in the egg box, but this is not necessary if you open the box periodically.

Maintenance Routine
Egg boxes are checked for moisture every couple of days.  Any water that may have evaporated is replaced by simply pouring water back in.  You can weigh the egg box to determine the amount of water to add, but I usually go by feel.  If you're using perlite, it's not necessary to remove the eggs or stir the mixture when adding water.  Just be careful not to get any of the eggs wet and the water will disperse evenly on its own.