Be yourself and enjoy yourself, first and foremost.
But do put in work for first year, as others have said, it might not count towards your final degree, but it will be built on in further years. Also, if you're a languages student, the uni look at first year results to help sort out your year abroad, so the better the grade, the better the options.
Also, be aware that Freshers' Flu can be late. I got mine mid- late October, after all the freshers stuff had calmed down.