Vacation schemes are famed for the variety of experience they offer. You'll be shadowing partners and associates, attending workshops and presentations and in most cases, doing a bit of real legal work too.
Between all of these activities, you'll have the chance to try your hand at networking. It's a skill that you might have developed a lot already, attending law fairs and participating in societies at university. But once you get into a law firm's offices, you'll really come into your own.
Most firms have a structured section of the vacation scheme that is devoted to networking. Networking events range from informal "ask the trainee" sessions to much more formal lunches at which partners and senior members of the firm might be present. The best advice is to prepare for anything!
It's good to go in with a brief idea of any questions you might have about the firm, as well as a vague idea of which partners will be attending and what areas of law they specialise in. That way, you're sure to make a lasting impression for all the right reasons.