"It can be hard to differentiate between firms, especially as so much of the graduate recruitment marketing material can appear to be very similar.
It's crucial you go beyond these to gain a full understanding of each firm. Use their corporate site for information about their deal work and also trade publications and directories like The Lex 100 (very useful for comparing firms).
Nothing beats actually meeting a firm though - this will give you a real insight into their work and culture, and what they expect from their trainees, so make sure you're aware of when they'll be visiting your university and / or any open days you can apply for.
Firms will expect you to know what they've been working on (and why this interests you), who their main competitors are, and what differentiates them from these competitors so research should be pretty in-depth."