Validity: Before you even do anything, first make sure that the exchange is available in your area. Eg. Coinbase, one of the largest exchanges, is not available in India and Indonesia. So before you do anything please check this.
Reputation: Next thing that you need to check is the reputation of the exchange. Are people happy with their services? Has it been hacked recently? How secure is it? Have people complained about it? Twitter and Reddit are good sources for checking this.
Exchange Rates: Up next we have the exchange rates. Different exchanges have their own exchange rates which may vary. Do your homework here and research 3 or 4 exchanges and their rates.
Safety: Please always choose exchanges which need some sort of ID verification from you. Even though they may take time, they are easily 100 times more safe and secure than anonymous exchanges. At the end of the day, it is your hard earned money. You must take that extra step to keep it secure, you can do your own research and choose your exchange, however.
