Hydration before the gun: Most people only think about hydration once they're on course, but the prep happens days out. Drink normally, plus a little extra, for the 24-48 hours before a big effort, and add electrolytes the morning of. Show up already topped off and you're not trying to chug your way out of a deficit once the gun goes off, which means less frantic drinking at every aid station and fewer bathroom stops eating into your time on course. Showing up dehydrated means you spend the first few miles playing catch-up instead of just running.
Hydration during and after: Everybody remembers to drink during a long run. Almost nobody keeps drinking after they stop, and that's the other half of the mistake. You're still sweating out fluid for hours after you cross the finish line or rack the sled, your body just isn't asking for water as loudly anymore because the effort's over.
The commonly cited sports-science guideline is to rehydrate with roughly 1.5 times the fluid weight you lost in sweat, not a 1:1 replacement, because you keep losing fluid through urine and sweat for a while after you finish. Weigh yourself before and after a hard training session if you want a real number for your own sweat rate, most people are surprised how much they actually lose.
Practically: don't stop at one bottle of water post-race, keep sipping through the next several hours, add electrolytes if it was hot or you were out there a long time, and use the color of your next bathroom trip as a rough gut-check, pale straw is the target, dark yellow means keep drinking.
Sleep and rest days: Training doesn't make you fitter. Training breaks you down, and rest is where the actual adaptation happens, muscle repair, glycogen restocking, and the nervous system resetting so you can hit the next hard session at full output instead of half-charged. Skip that part consistently and you're not being disciplined, you're just accumulating fatigue until your body forces the rest on you anyway, usually as an injury or a plateau you can't train your way out of. Sleep is the single biggest lever you have, most endurance and hybrid athletes in hard training blocks need more than the standard 7-8 hours, not less.
Active recovery and mobility: A rest day isn't a guilt day. An easy walk, gentle mobility work, a light spin, keeps blood flowing without adding load. And if a scheduled hard workout feels off because you're still beat up from the last one, moving it is a training decision, not a failure. The athletes who stay healthy through a full training block are usually the ones who treated rest, hydration, and mobility like sessions on the calendar, not afterthoughts, so the body is actually ready for the next hard effort instead of running on borrowed legs.
General performance guidance, not medical advice, if you have a health condition that affects fluid, electrolyte balance, or sleep, check your recovery plan with a doctor or sports dietitian.