Hi there,
Before you get your geckos, you should buy a copy of The Leopard Gecko Manual by de Vosjoli et al. It is an excellent resource that will help you prepare for and properly maintain your geckos.
Along with the advice you have already received, I would recommend that if you are buying young geckos (still growing) then you should house them separately at least until they have reached their adult size. If they are a pair (male and female) then you should house them separately until they are ready to be bred (the female needs to be over 9 months old and over 35 grams, minimum - most people prefer older and heavier). If you have a pair of young females and really want to house them together right from the beginning, just make sure that each one is getting enough food. Their growth rate is very closely linked to their food intake when they're young.
I hope you will enjoy your geckos, once you get them. Most people find them rather addictive!
Regards,
Amy