Pack a set of warm clothes in your race-day bag.
At the end of the race, you will be sweaty and possibly a little chilly. You will want some dry clothes to put on over your sweaty ones. The best bet is to pack loose-fitting clothes for the end, as you may be too tired to fight with tight sleeves or pant legs. Plus, if you need to take your sneakers off, it may be difficult to get them back on. If for any reason you can't pack clothes in a race-day bag, make sure family or friends carry some for you when you meet up with them after the race.
Bring some warm clothes that you can throw away before the start.
Many big marathons have you report to the starting village well before the race starts. In the early morning hours, you will need some clothes to help keep you warm. Most races will have you check your race-day bag quite a while before the start. Be prepared to discard your last layer of warm clothes just before you start. You will not be able to get these clothes back.
Use the port-a-potties before the race starts.
Even though lines can be long in the start village before the race, use the port-a-potties. This one piece of advice can save you 10 minutes on your finishing time. If for some reason you can't manage to go before the race, plan to run past the first or second aid stations, as the port-a-potty lines at these stations will be enormous. The further you can make it without stopping, the shorter the lines will generally be.
Have a strategy for when to enter your race corral.
If you want to be as close to the starting line as possible, enter your race corral as soon as it opens. Be aware that you may then have to stand in the corral for quite some time. If you prefer to hang back and not fight with the crowds, then wait 10 or 15 minutes to get into your corral. You may still have plenty of people around you at the starting line due to the corral behind you, but you won't have to fight with others in your corral.
Bring your mobile phone with you.
If at all possible, carry your phone with you so that you can communicate with family and friends during and after the race. This tip is not suggesting that you have long, drawn-out conversations while you run the marathon, but rather that you use your phone as an added way to find your family and friends along the route. You should, of course, map out where they will be before the day even arrives, but having your phone will mean that you can communicate with them even if plans go awry. Especially if you're running in a big marathon like New York or Chicago, having a way to talk mid-race can be a big help even if all you discuss is which side of the street they are on.
Run past the first table and first volunteers at every water station.
Most race participants will flock to the first table at the water stations. If you run a few feet farther, you will find plenty of water without a lot of people to dodge. There will also be volunteers throughout the entire station, so run past the first few and look for the ones that look long forgotten. They will be happy to hand you a cup. Slow down to a walk to drink unless you're an expert at drinking on the run.
Run to finish, not for time.
Many first-time marathoners get so caught up in finishing in a set time that they either bonk big time or don't enjoy the experience at all. The point of your first marathon is to finish with a smile on your face and the desire to run another. You'll have plenty of chances to improve on your time, so just relax and enjoy your first marathon. No matter what your time, you'll be able to say that you are a marathoner!More: 5 Tips for Marathon Pacing
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