Your crested gecko will need to be fed twice a day. I feed my crestie crickets in the morning and Repashy MRP in the evening. Crested geckos are picky eaters and will not eat everything you offer to them. It also takes time to change your crested gecko's diet.
To change your crested's diet, you will need time and patience. Since crested geckos will not starve themselves and will eventually eat what is offered, continue offering the same thing at every meal time. Eventually, your crestie will be eating the new food. However, one product I strongly do not recommend is the new Fluker's Crested Gecko Food. It's advertised as "Easy to eat Spherical Granules that Crested Geckos will actually eat!". It is a horrible diet for crested geckos that has little to no fruit in it and is mainly vegetables, which are not a balanced crested gecko diet. Also, crested geckos will not touch it. Don't try to make your gecko eat it because geckos just won't eat this stuff, and you will end up the one starving your gecko.
Crested geckos can be tamed to handling, unlike other species of reptiles. It will take a lot of time for your gecko to get used to being held. I've had my crested gecko for a while, and he's still not totally used to handling. I suggest letting your new crestie rest 4-5 days after bringing it home before trying to handle it. After that, you can slowly introduce handling at 5 minutes per day (or less) and gradually adding time to that once your gecko is more comfortable. These geckos can jump, climb, scale walls, and cling to screen ceilings with ease! Remember that while holding your gecko. Also, remember that any animal with teeth can bite. I've read of some owners getting bitten by their geckos, though it's rare and mine has never done it to me.
The only way to make your gecko thrive is to have the correct heating, lighting, and humidity levels in your gecko's habitat. The temperature should be maintained (and is best at) between 72 and 80 degrees F during the day and should become no lower than 65 degrees F at night. Lighting is not necessarily needed for the geckos, but a heat lamp is. You should also mist the entire terrarium with water at least twice per day and make sure the humidity is maintained over 55% (you'll need a hygrometer) at all times.