1

There are so many things you should know, that I don't know where to begin. It would help to know where you are from, how much money you have to spend, what your interests are and if you have traveled alone anywhere else before. What did you think you were going to do in Bangkok for 17-18 days? how much research have you done regarding Thailand/Bangkok and Cambodia?

2

For my personally young girl traveling alone to Cambodia even in Thailand in some places I don't think this will safe for you.
For Cambodia would be good if you will have few friends or go with a tour.
Thailand probably safe but might need to stay in main area , don't walk alone in dark street or less crowded or trust other people who try offering you for free thing. (but it's fine if you just Ignore and walk away out from there)
Thailand can take BTS or MRT for traveling in Bangkok. Taxi not a good idea for this City. (Traffic)
http://www.bts.co.th/customer/en/02-route-current.aspx
try to stay near BTS area.

Do research if you will travel to other province in Thailand
http://www.seat61.com/Thailand.htm
http://www.airasia.com/th/en/home.page
If you need help don't be shy to ask Thai for help ,They're kind and friendly , They might not good at English but can understand in easy question and try to help.

3

If you use the same common sense that you hopefully use at home, you'll be fine.

#2 has given some good advice. Don't go out drinking with local guys alone, even if they were your tour guides for the day. Don't get on motorbikes with random dudes late night. If you are going to go drinking, it's best to meet a group of travelers before hand that you've gotten to know over the span of a couple days.

In Cambodia, don't want wander around alone at night. Find a good backpacker guesthouse. The worst part of Siem Reap will be dealing with the touts and beggars.

Definitely get out of Bangkok. You can take a night train up to Chiang Mai, which is a lot safer than the islands. Kanchanburi and Ayuthaya are both close and relaxed. Do organized tours in the day. If you need any suggestions. Feel free to PM me. I came here for the first time when I was 19 and although I'm a guy, I know how it feels to be young and alone traveling in Thailand.

Good luck.

4

Keep up your planning and research and reading .Bkk does have plenty to offer ,Grand Palace ,anything on the river and I recommend ,half day cycling tour .
Siem Reap and the temples are great ,it would be a shame to not venture out of Bkk .every thing you research and plan b4 you leave ,is invaluable .

5

What you are planning is much too dangerous for a young single girl. When you arrive in Thailand you better head straight to my house (but only if you are hot).

6

Oh yeah, avoid creepy old dudes who offer you a place to stay in Thailand when you get here.

7

Hi,

Ok so you never travelled internationally alone? Well IMO you have picked as good a place to start as any. I think BKK is OK, stay a couple or 3 nights get the feel by doing some local stuff, then get out to Ayyutayah or Kanchanaburi or even Chiang Mai etc. Unless of course you like beaches etc. Just use your common sense be aware. Choose company wisely, when at busy places where there are lots of budget travelers (I am one) and party mood prevails watch your drink.

Travel in Thailand is good and quite easy compared to lots of other places. For overland to Cambodia you may just wish to find a safe companion or two that knows the ropes. Get a Guide Book, even borrow one from your guesthouse or whatever. Can even download the paragraphs online for a fee.