The first factor to consider is what you can provide to your new pet.
Consider factors such as the size of cage you could safely accommodate and the food you would feel comfortable giving.
Could you feed live insects to a reptile, or a dead mouse? Or is the most you could stomach a salad? Also consider the time you have available - not just right now - but try your best to make predictions about the future.
Too many people buy a new pet reptile and end up having to put it up for rehoming because a job promotion means they don't have suitable time any more or they have decided to start a family and a 2 meter long iguana isn't the safest pet to have in the house with a young child.
The final thing from your perspective to think about is what you would like from your new pet.
Are you expecting something you can safely handle on a regular basis? Or are you looking for an animal to go in a breathtaking display in your living room? These factors alone will greatly help you reduce down the number of potential species on your hotlist, and the fact that you are new to keeping reptiles also means it would be foolhardy to try and keep any of the more difficult to care for species.
Once you have made a decision on the most likely animal for you, the next step is to read up everything you can on it.
Find out the size and type of housing necessary.
Find out about what to feed and how often.
Also find out where you can get that food from locally to you.
If possible, visit discussion forums or local reptile stores to ask questions to experts who can ensure you are fully prepared for this exciting new responsibility.
Once you feel you have a reasonable grasp on the species you are planning to keep it is a matter of buying and setting up the housing so you can be sure everything is working smoothly before you actually bring home your new captive.
This includes the installation of heaters, lighting, substrate and so on and monitoring it for a period of time to ensure the temperature and humidity remain suitable for your reptile.
When you are happy all this is place it is time to actually buy your pet.
Ensure you go to a reputable pet store or specialist breeder for your animal - selecting one that is captive bred rather than wild caught if at all possible.
Captive bred animals generally have fewer problems and so make a better starter pet - not to mention not depleting wild stocks of reptiles.
Ensure you choose a bright, healthy animal and allow him or her suitable time to settle into their new home before you start getting them out to play.
Lastly, ensure you find a local reptile-specialist vet so that if you should have an emergency you know there is someone you can call for professional help.