OK
Tigerr kinabalu and anyone else who still have your SSN, here's a quick howto

What you need
a. credit score
b. credit history
c. bank account
d. US forwarding address
e. time & some money

For a. and b. go to creditkarma.com and creditsesame.com and sign up for accounts. You'll need your SSN and will need to remember some old addresses that you've used before, even if it was 20 years ago. You may need a VPN based in the US too. Check your credit scores (pref > 700) and read up the recommendations.
The rest are self explanatory.
In general many credit cards will give you a certain amount of miles after signing up and completing a certain amount of spend. Example is Chase British Airways Visa card, spend US$1,000 within 3 months of signing up for the card and you'll get 50k Avios miles. Many cards will have higher spend requirements. I use these cards for everyday spend in Malaysia to reach the spending requirement.
For comparison purposes, KL to Phuket/Saigon/Phnom Penh is 4.5k Avios miles + ~US$8 one way on MH economy.
Lots of other info on flyertalk, or next time I'm meeting
tinkerbel for drinks I'm happy to share more details.