Lol, people are exaggerating here so bad. You don't have to revise super hard all year, just make sure you keep up to date with what is going on in your classes all year. I did like.. literally zero revision for any of my subjects until my mocks in like February. And you don't need to give up your social life, that's ridiculous. A-levels really aren't that bad, there's just a lot of info to take in but you have a huge excess of time, especially if you're asking this question in AUGUST.
About 3 months before exams, start properly revising, doing past papers, just really hit it hard, until you're at the point when you know every single thing in your specification and you basically have to get an A*. It takes a lot of time, but it's not too bad if you're organised.