Running the London Marathon this weekend? This is for you

Entering the ExCel centre to register will simultaneously thrill you beyond words and leave you totally petrified.

Nick Webb, on Flickr

The marathon theme will play as you go under an arch of ballons, and it will hit you: I'm actually doing this. You'll come out with a red kit bag, a timing wristband you'll probably never look at again, and a stomach full of free pasta.

You'll try to go to bed early on Saturday night but you won't be able to sleep

Alyssa L Miller, on Flickr

Leave yourself something to do, like drawning your name in really big letters on both sides of your running top.

You'll be amazed by how friendly a crowd of thousands on a train platform can be

Joe Kingston on Flickr

Especially when your guard sees the approaching train and shouts "Oi you! with the red bag! Behind the yellow line!"

You'll worry about missing the start because the queues for the toilets are REALLY long

Francis Storr on Flickr

Not going to lie: they are really long, and if you don't really have to go, don't (there are toilets on route too). But if you get stuck, don't panic - the timing chip on your shoe starts when you start. My first marathon I missed the start proper and jogged over the line at the very back. It was fine. Quiet, but fine.

Your "reminds me of the marathon" song won't be the one you expect

There are a lot of pubs and bands on route, playing a wide variety of music, from Bruce Springsteen to Britney Spears. One of those songs will be the one that encapsulates your marathon and you've got no way of controlling what it is. Mine's Proud by Heather Small. Such fun.

You'll be really impressed by the first celebrity you spot

Shimelle Laine, on Flickr

Then you'll see another one and another one and another one and eventually you'll stop noticing. Worth keeping an eye out for Paula Radcliffe on Sunday, mind you.

You'll constantly be humbled and moved by the courage and spirit of the human heart

Julian Mason, via Flickr

Yes, it's sappy. But everywhere you look there's someone doing something amazing: the runners in costumes that make it three times as hard, the stories you'll read on the back of other people's shirts, the runners who look out for you when you really feel like you can't go on - and at mile 20, as you're coming back along the Highway, the hundreds of people still on their way out to Canary Wharf, who will make you feel a million times better and also amazed that they look so cheerful in the face of the miles they have left to go.

The worse you feel, the more amazing the crowd will be

Pete Sheffield, via Flickr

It's fair to say that the faster you can run the marathon the easier it is - the longer you're on the road, the tougher it is on your body. But it's also true that the crowd works hardest for the runners who are working hardest. My most painful marathon was also the most enjoyable - because the support of the spectators lifts you off the ground just when you think you can't do it any more. (Just make sure you've got your name on both sides of your shirt.)

You'll accept sweets from strangers

Jono Takes Photos, on Flickr

You know your mum taught you not to, but somewhere between miles 16-19 someone will offer you a jelly baby or a slice of mars bar and you will love them more than you've ever loved anyone in your life.

Someone older than you will sweep past you at mile 24 and make it look easy

Kai Chan Vong, on Flickr

Birdcage Walk. Me, huffing like I'm about to have a coronary and feeling like it's never going to end (see point below). A man in his sixties runs up behind me going twice the speed I am, sees I'm struggling and slows down. "Breathe it out," he says, demonstrating what he means by blowing out in a controlled fashion. "You can do this, it's easy from here. Breathe it out." He waits ten seconds to check I've got it, then runs on. It's hard to explain what that meant to me, without sounding stupid, but I still say "breathe it out" to myself whenever I feel like giving up.

You won't believe how long it takes to get to Buckingham Palace

Nicholas Schooley, on Flickr

There are a lot of trees on Birdcage Walk, which means you can't see where Buckingham Palace is. It feels likes it goes on forever, and then you sweep round the corner oand there's the finish line and everything is amazing again.

The moment when you turn the corner and see the finish line will be happier than you can possibly imagine

Tomasz Dunn, on Flickr

You made it. You could crawl from here and you'd still finish. Don't, because that would hurt. But take heart from the fact you could.  

You'll spend the rest of the day exchanging knowing looks with other runners wearing flip flops and carrying finishers bags

Satish Krishnamurthy, on Flickr

In the pub, on the train, hobbling down the street: the telltale walk of a post-marathon marathoner will catch your eye wherever you go, and you'll feel it all over again. 

You'll lose a toenail

Don't worry about it. They grow back.

You'll want to do it again

Chris Barber, via Flickr under Creative Commons

A million good lucks to all of you running on Sunday. You'll be amazing.