In addition to all the advice given so far (which is good) allow me to add a few other things:

1) If you're going to use the net for hookups make a separate email account. Make sure the name and password have no connection to an existing account and NEVER use this to email regular old friends/family, etc. This will prevent you from accidentally emailing your mom/sister/boss nasty stuff.

2) Patience is your friend. When you post CL ads, hold the responders to some standard of intelligence. And if they don't place some value on typing properly to communicate ideas then they don't expect YOUR responses to be sharp. Any animal can get a mobile phone, hit the web, and respond to ads so if she's not screening properly on her end it's a big red flag on her ability to calculate risk. It throws into question how many guys she's hooked up with, if protection was used, if she have no problem going to a strange guy's place for the first meeting, etc. Generally speaking, you should sense a bit of caution/hesitancy on her end. That's a good sign she's not banging guys ever day of the week that she's met online. Be a gentleman, take your time speaking with her, take her out for a dinner or drink and show her you're not a mongrel.

3) In my experience the girls you want to find on CL or Fetlife or whatever are regular, educated, well-rounded people that just use the net to find likeminded kinksters. If you don't get that sense, stay clear.