Get a spare mobile number for OLD. Protects you against Mr Nice Guy (or Gal) who later turns out to be a lunatic or worse. Never give out facebook details or anything else that could trace you in the real world, unless you are sure about them (a few real world dates at least). I had a would-be stalker once (not OLD) and it was horrible to feel spied upon.
If you start chatting, find out why they are single and about past relationships...how people talk about their ex's is very revealing about who they really are. Vindictive people get very carried away and won't hesitate to paint a picture of their evil ex and how they were wronged. Two sides to every story...
Try the 'met anyone nice here?' question...if they have met dozens of unsuitables in person and are very critical about their dates, run for the hills. Lots of narcissistic types on OLD and social media looking for validation of their superiority to the rest of the world.
Never meet anyone you are not certain of (just to be nice), and don't take anyone home on a first date unless you are prepared/ accepting that it might just be a one-nighter. Chatting online creates false intimacy that you 'know' them.
If they are evasive about meeting up, tread carefully...could be a scammer, married, serial chatter or other non-starter situation. Expect that people will lie about their circumstances and if they don't, there is your keeper.
Ask about hobbies, work, travel experiences...helps you to build a picture of who they are, and how suitable they are for your lifestyle/ interests.