frequenttraveller
Oh yes, I get you on the one things leads to another (and on and on ad infinitum).
I sometimes bounce on and off the wagon (and this bus). It's been a long time now so I have some tried and tested strategies that work for me - we each have to find our own ways, but using other people's examples can be a great way to start.
If I've newly climbed back on board, I often find it easiest to avoid drinking situations until I've 'settled' and feel a wee bit more confidant about my resolve. Day 1 is probably not the time for that 
There have been many day1's for many people, all undone by being unprepared for a social situation.
The easiest way out for me is to offer to drive. I live in Scotland where we have lower driving alcohol limits so it is very widely expected that the driver will have no alcohol. I feel good about running other people home too, and accept their gratidute in exchange for meeting up for coffee.
In the early days (and only you can decide whether that is one week, 4 weeks, 3 months or whatever), I avoid totally anything that is a real drinking session. A group of friends meeting up with the sole objective of getting pissed - I 'get' a sudden violent stomach upset and call off. A drunken hen weekend in Ibiza - I can't afford it, or I can't get time off work. I have to admit I'm 60 and I've never been invited to a drunken hen weekend in Ibiza
But we have to socialise, we have to be able to be in the company of others, we have to learn to enjoy ourselves without alcohol.
For me, it starts with 2 things: resolve and planning.
Resolve first: So, for example, you've been invited to a friend's birthday on Friday - that would be (perhaps?) day 7 for you - a whole week without drinking! Amazing, what an achievement. So why would you let that be derailed? You are there to celebrate her birthday - yes, that's by turning up, hugging her enthusiastically, maybe buying her a really thoughful gift. All of those things will be remembered and enjoyed.
Will you actually enjoy a glass of sour, fizzy, over-priced prosecco? Really the sickly, sweet, taste of it? Would a soda water and lime be as good? Would you enjoy the end of the evening where you'd forgotten what you were here for and ended up blubbing about your own broken heart (Oh yes, I've been there!)
Would your friend appreciate that you'd made the effort to be there, and to be happy and delighted to celebrate - yes of course! Would she appreciate that the end of her party night was spent cleaning up vomit? (Oh yes, I've been there too 
)
Of course neither of these might be you, but they have been me. And knowing that, and acknowledging that gives me the resolve I need, and the determination that this time will be different. That's where the planning comes in.
Planning: I'm determined to stay sober but as I anticipate the event what are the decision points. Maybe others are having a pre-loading session - "Sorry I have to put the kids to bed / finish an assignment / get back from visiting MIL... I'll see you there"
Make sure you arrive really well hydrated, there is nothing like dehydration to make you grab the first (alcoholic) drink and down it in one. So plan meticulously on drinking tea, herbal teas, water, juice, throughout the day. As much as you can.
KNOW what you are going to ask for for your first non-alcoholic drink, and what you're going to say around that. So when the mythical birthday girl welcomes you waving a bottle of something, you greet her enthusiastically and say "Oh Fab, but I've come on the bus/tube/walked and I'm freezing - I'll just grab a coffee first" OR "That looks wonderful, save some for me, I've been out all day and I need a big glass of lemonade first".
You'll will know the kind of things that sound natural for you.
Repeat, repeat, repeat. Every time you succeed give your self a little pat on the back. Or log in to mumsnet and tell us! We will cheer for you.
After a couple of drinks no-one will notice or care what you are drinking, and you might start to notice that others are getting a bit loud or repetative. You migth find it mildly amusing, you might even find you are glad not to be part of that particular mood.
Alternatively at a dinner, I set myself a target - I will not have a glass of wine until I have had at least 10 glasses of water. I pretty much find that after that quantity of water drinking anything else has become quite unappealing.
And for me the final part of the planning is how to leave. "Sorry. I've got a terrible headache, it's been a great night, call you tomorrow" OR "George just called and the baby is sick, I'm going home to help, enjoy the rest of your evening". Or just slip away. If it's a real big event most people won't notice. Text host and say "great night, thanks xx" At the point at which you're leaving it's not about you, so don't stress about it.
But do know (for yourself) when you plan to leave - after the present giving, after you been on the dance floor once, at a particular time. And stick to it.
And plan a reward for when you get home. A hot milky drink and a hot water bottle, a cup of tea and a chat with your partner, a hug with your kids or your dog, 5 minutes spent looking out at the lights of the town, or the stars in the sky and being in awe of it and your place in it.
And the next morning - Wow! You did it. You got through it. Did you enjoy it? maybe or maybe not: would you have enjoyed it if you'd been drinking? maybe or maybe not. But you're not puking or sick or shaky.
Apologies for the epistle! And I've sent to a PM