How careful you are in your preparation should match the destination, as racing in a major European city is far more predictable than one in Africa.
It's about planning accordingly and here are some of the most important things to consider...
Running at altitude
You should either go at least ten days before to acclimatise or fly in and race within two days. It's the period in between when your body is adapting when you should try not to race.
The heat is on
For marathons in heat, the longer you can be there for in advance to adapt the better. And there are heat chambers in Universities such as St Mary's or Kingston University - five to six sessions should do the trick, but even sessions in a sauna or running with an extra layer can help.
Carry on essentials
You can nearly always borrow kit, but if you're very specific about what you wear then carry it in your hand luggage, especially your trainers, as bags do go missing at airports. Even if you eventually get the bag back, the stress is the last thing you need before a marathon.
Back up plan
I leave nothing to chance with marathons, so always take at least 24 hours worth of carbs with me, so that I can eat to my schedule and not one set by a tour guide or dictated by the shops I find.
I'll eat dinner almost anywhere, but came unstuck in Afghanistan and Sierra Leone by eating something that flushed me out and I struggled as a consequence. Imodium is a must in my pre-race routine anyway, but even more essential abroad, it has no negative impact on you and gives you peace of mind.
Expect the unexpected
The less established a race, the less predictable the course, so be aware that mile markers may be creatively placed, fuelling stations may disappear and the actual distance could be a little generous. So pack enough gels for the race and try where possible to expect the unexpected.
Experience over time
Be realistic with your target time. If you are going to a country with 90% humidity and 35 degree heat your time will be significantly slower, how much is dependent on the person and the conditions. Start slowly and ease into the run. Forget about PBs, think experiences.
Whether I'm being overtaken by Afghans who went through the halfway point in world record pace, due in part to the help of a motorbike, or bartering for water with a pregnant women from a well, international races offer experiences that cannot be matched from a simple road race.
So while I may be painting a picture of potential horror, it's the unpredictability that fuels the adventure and create the stories which make international races so memorable.
So prepare for the worse and embrace the chaos, as it's the chaos you'll be taking about for years to come and not the finish time.
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