Becoming fluent on your year abroad is easy as pie if you're constantly surrounded by local people at work, at university and in your social life, but in reality your 'year' abroad might be only seven months (or half of it spent in another country), you might also hang out with English-speaking friends while you're there, and of course you always need a bit of time to yourself! There's no way that you can be fully-immersed 24/7, but you still need to appear less foreign/touristy as fast as possible. Why? So that locals don't reply to you in English, so they trust you and open up to you more, and so that you feel you are progressing quickly which helps hugely with confidence. "Your [insert language] is amazing! How long have you been here for?!" We are all, secretly, praise junkies.
You'll notice I haven't mentioned language skills. I'm not talking about your extensive vocabulary or grasp of grammar - they require study and immersion to perfect, and everyone will be at a different level. What I'm talking about here is faking your French/Italian/German/Russian/Chinese/Spanish-ness so that you can fit in easier and learn faster. How? You need to be incredibly observant. Notice and remember hand gestures, mannerisms, repeatedly-used expressions, intonation and how locals do regular things like ordering coffee, buying bus tickets and leaving their cutlery at the end of a meal. As you pick up these habits you will feel and become more local, and this is a successfully tried and tested technique!
During my year abroad in Italy I did my absolute best to appear Italian through what I wore and how I spoke, making a special effort with my accent and dialect. In Florence I noticed that they say 'h' instead of a hard 'c', the famous exemplary expression being: "hoha hola hon la hanuccia" (Coca Cola with a straw), they use more of a 'w' than a 'v' (e.g. "non lo woglio") and a bit of a 'th' on their double ts too. Once I had worked that out, my transition into sounding like a local was a lot easier - things like saying 'eeeeeeh' instead of 'ummm' when I was mid-way through a sentence, and adding words like 'beh, 'boh', and 'eh'. A LOT. I also tried to pick up the hand gestures, shrugging and intonation. There is a very specific way in which Florentines say "Macchè dici?!" (what are you on about?!) - a very common phrase in Italia, seemingly. Their hands and wrinkled brow implore reason and their voice sounds absolutely incredulous as if the person on the receiving end was literally born yesterday; "Mahhè deeeeshi??!" they ask.
Finally, here is a useful and very funny video which @TheDanCash alerted me to, and which I think enhances my point...
In bocca al lupo! :)
P.S. I just found another one. Eddie Izzard's Survival Guide to French: