Yeah, avoid tuk tuks - in bangkok. They might look like fun - until you get in a crash! In smaller towns they're probably fine though.
I think a good rule of thumb is - if any Thai person approaches you cold in the street - strikes up a conversation and it ends up with them asking you to do ANYTHING at all (particularly go somewhere with them or meet them somewhere) then it is a scam. They are good at targeting newcomers to the country. It doesnt mean you're going to get killed or robbed, probably just scammed of money!
I'd go to Khoasan road if I were you for a start. Arrive in the daytime if possible. It's easier. But either way - find a guesthouse online - I'd recommend New Siam, Merry V, Rambuttri Village or Four Sons. Telephone them in advance and book a room - then ring the day before you leave to confirm your reservation! Get a metered taxi from the airport or the airport bus to KSR.