The London Art Fair is now celebrating its 25th year as a major event for modern and contemporary British art. With four levels and over 100 galleries exhibiting works by their top artists, visitors can expect to be overwhelmed by the amount of work on show. An art fair's purpose is, undeniably, selling art – often painfully clear from the way gallerists seem to hide inside an invisible soundproof box whenever I, not at all resembling a rich collector, approach a booth. But there are many less commercial projects, performances and other happenings that also make the London Art Fair attractive to casual visitors.

Up on the fourth floor of the Business Design Centre, Islington are the Art Projects – a curated showcase of London's leading contemporary galleries. This is the place to start for a sample slice of the city's emerging artists and artist-led spaces – as well as works that do not traditionally make their way into art fairs. Check out some well-known contemporary names such as BEARSPACE (a Deptford pioneer since 2001), Limoncello (one of the organisers of last year's Sunday Fair), Ceri Hand and The Wapping Project Bankside. Whitechapel Gallery are also displaying a selection of artists including Gillian Wearing (My Hand), Zarina Bhimji and Alice Channer.

ALISN (Artist-Led Initiatives Support Network) have set up a fantastic project in the LAF Projects space to critically examine the art fair as a commercial fixture. Their booth, SUBLET, has literally sublet space to twelve artist-led galleries, as well as film and performance artists – and gives emerging and promising new artists (usually housed in industrial areas or neighborhoods off the beaten track) much-needed exposure. From one of these, Occupy My Time Gallery, Shona Davies and David Monaghan's Uninvited series (2012) was particularly memorable: three coloured boxes with tiny windows turn the viewer into voyeur, as you peep into a room and watch intimate and unsettling animated scenes unfold.

Julia Vogl's PREDICTING – The London Winter Weather, displayed by Hoxton Art Gallery, is a charming and simple piece: here you can tie a coloured ribbon onto strings representing each day of the fair with your prediction of the weather. I chose a bright green "Raining like a cow relieving itself" ribbon for Thursday – whether or not the weather agrees, it's a cute idea and added a touch of fun to the fair.

Patrick Hughes' disorienting relief painting was stopping visitors in their path: it is a series of corners and doors that seem to wobble and move. As you approach the piece, it resolves itself and the veil suddenly drops. The mirage-like doors, almost unbelievably, are protruding by a good six inches – a fascinating optical illusion (at the Flowers Gallery booth).

It's also worth taking a look at Photo50, the guest-curated section on contemporary 
photography – including works by Dorothy Bohm (whose Women in Focus exhibition is still on at the Museum of London).

These are just a few of the fair's many highlights, but the London Art Fair runs until Sunday, so there is plenty of time to take a wander through and see what catches your eye. Although it's often very tempting, you don't need to be in the market for a Picasso to have a browse – there are plenty of hip young visitors swanning about, whom I suspect are at least partially here for the free drinks.

London Art Fair 2013, at Business Design CentreKate Mason reports on the London Art Fair 2013.