Hi Kellinicole,
Eggs that are fertile will often look healthy being of a nice white color with a slight leathery feel to them (depending on the substrate laid in some eggs may have an off-whitish appearance this is no worry). The honest best way to tell will be to very carefully candle your eggs with a small L.E.D. flashlight
(sometimes 1-2 weeks later after laying to get best results). Other lights will work but a controlled beam of a L.E.D. will do the best and you can pick one up cheap at your local hardware store or wal-mart. Hold the egg very carefully without turning it the slightest, after the first 24 hours from laying the embryo starts to set. If all is well with your eggs the embryo will be at the bottom of the egg containing a portion of amniotic fluid(Yolk) and a thin air sac at the top of the egg. If you notice a little red vain inside the egg then chances are it is fertile but you will still want to watch very closely the next few days. If any of the eggs collapse you will want to remove those as soon as possible without disturbing the other eggs (not to be confused with natural dimpling before hatching). Also another worry will be mold and fungus so be sure to keep an eye on humidity/Temp levels and adjust appropriately. I usually recommend 75-80% @ around 84.5f to 86.5f. If you encounter mold this is usually a sign of infertility if it only effects one or two eggs but this is not always the case. If you catch mold early on you may be able to solve this by removing the lid to the container in incubation. I also have a method for fungus but will not post as it will start a "heated debate". Please check my post about sterilization of substrate for laying and incubating as this will greatly increase your chances of success. I hope this helps please let me know if you need anything. P.M. with any questions about the fungus issues that some encounter. Peace J