When I was 20 I left London and moved with my then wife to work in Bahrain (small Island next to Saudi Arabia). I did have a job to go to however and knew a couple of people working there.
A few years later, I moved to Kuwait, again I had a job, a wife and I knew a couple of people (not well) in the office.
3 years after that we moved back to Bahrain, again job was in place and I knew quite a few people via business and sport connections.
After 4 years and we moved (with DD aged 4 and wife preggo) back to England. Again I had a job and a family and knew a few people in the area where we settled which helped.
Very soon ( hopefully by end of Nov) I will be moving to Fl, finally getting married to fiance Jana ( after long distance romance and visa delays) where we will be setting up home ( with her DS aged 10). This move is potentially the most difficult I've made as 1) I don't have a job sorted out yet ( not allowed to apply until work visa is through) 2) We don't really have any friends or family in the area 3) Jana doesn't have a job yet.
I do however plan to use the experiences I've picked up over the times I have resettled as most of them are useful. Here's a list of things I think are helpful/important when relocating, some of them deal with moving countries, but I'll include them anyway.
1) Register with Embassy/Consulate. Granted not relevent in this question, but for anyone moving country this should be #1 priority AT ALL TIMES. If you get into trouble, your embassy will need to be notified, if you've registered beforehand it helps them deal with you MUCH quicker. If there are political problems in the area and you're registered, your Embassy can contact you and help with evacuation or advice. On a social note, many Consulates and Embassys have social activities that would give you the opportunity to meet fellow countrymen and women in similar situations (particularly important for non working partners in a relocated family). In the early days try to attend ANY social activity they are running, even if you aren't that keen on the activity. Chances are you'll meet someone in EXACTLY the same situation as you. Neither of you may like the activity being run, but you'll probably find something that you do both have an interest in and would be able to meet up at a later date.
2) If you have a sport you participate in (tennis,golf,raquetball, bowling etc) make sure you find a club to join, sign up to any leagues that are available and start playing and meeting people. Even if your social life doesn't improve, you'll get fitter LOL. I was lucky I was a keen rugby player and the Gulf states in the Middle East had a thriving league. Rugby's a very social game and the day trips to other countries to play games was an excellent chance to meet people and build friendships. Golf is probably the best game to meet people and build up a social network in a new location.
3) Once you've found a job, look for work related social activities. Again , even if it's not REALLY your type of thing, theres a good chance if you go along you'll meet someone who does share an interest.
4) Make the most of any time you do get to explore your new surroundings, get to know the area and get to know where interesting activities take place (even if they're not 100% your interests). This will not only provide you with an opportunity of meeting people, it will also give you things to talk to other people about when you make new friends at different social activities. There is little as effective as killing a conversation with new work colleagues as when asked " Hi X, how was your weekend, what did you do" to respond " not much, watched TV Friday night and all day Saturday, did laundry Sunday morning and watched CNN all Sunday night". A visit to an art gallery, the theatre, sight seeing, restaurant or music venue is much more likely to get them to ask about what it was like etc, and you may find someone who's interested in those things will come up and ask you about the details. Giving you the chance to suggest they join you next time you go.
In my time abroad I saw PLENTY of people arrive, some settled easily/immediately had a great time and enjoyed themselves, some took a little more time but relatively quickly settled and made friends, and some NEVER really settled were terribly homesick and were happy to leave at the end of their contracts. As a pretty decent rule of thumb, the people who didn't settle had already made their mind up before arriving they weren't going to like it. Invariably they expected other people to invite them to dinner parties, functions or activities before they reciprocated. Usually they weren't keen to join sports teams nor did they put themselves out.
In life, I feel what you ultimately get out , is directly related to the effort you put in. This holds as true in social life as any other. The more time, effort and invitations you put out, the more responses and reciprocation you will receive. Sport, art, music and theatre are among the easiest routes to build up a social circle in a new location. It's worth remembering that by broadening your horizons and being prepared to try something you would not normally have tried makes it MUCH more likely that you'll get the opportunity to enjoy some company with not only those activities, but also the ones that are closer to your own heart.