My biggest tip is to ignore labor as long as you can. The less energy and attention you give it, the more you will have to pull from when you really need it. I've had clients use many different techniques to ignore labor. Some go shopping, some cook or bake, I've even served a client who played video games.
Keep your routine normal. If you are in labor and it is your normal time to go for a walk, then go for a walk (you might want to go for a shorter walk, or have a pace that is slower than your usual pace). If it is time to go to sleep than get in bed and try to get some sleep. Even if you aren't able to sleep but you can rest and relax, that will be beneficial and let you have energy for the long haul.
Keep your activity levels low key. Labor is not the time to head to the gym to try a new HIIT workout or go outside and thatch your 1/4 acre lawn. By being mindful of your activity levels, you will be in a better place to have the energy to finish labor strong. When you are worn out at the end of labor, it can create challenges in the immediate postpartum such as increased risk of hemorrhage, difficulty getting up safely to use the bathroom, and you may not have the energy to truly soak in that you have a brand new baby in your arms.
Eat and drink. Long labors require lots of calories to keep going. I don't expect clients to eat full meals, but I do want clients to eat. Small, frequent snacks are what most clients do so have some easy snacks and light food on hand. Some ideas are fruit, yogurt, cheese, jerky, crackers and nut butters, nuts etc. Drink plenty of liquids to stay well hydrated. Have a grazing mindset, and eat something every half hour when you are awake. I also like it when whatever you are drinking has some calories. Watered down electrolyte drinks, coconut water or homemade laboraide are fine ideas. If you want to drink juice or soda, I'm fine with that too.
Sleep. I know it sounds hard, but you can sleep during labor. I've been at many births where the client is able to doze off between contractions. I always find it interesting that if Mom is really tired and lays down, labor slows down. The body recognizes the need for sleep and accommodates it. If you can't sleep, but you can rest and relax between contractions, that is so very beneficial to replenish energy and get through to the end with some reserves.
Pace yourself. To make it through a 24 hour or longer labor with some reserves to finish strong, you need to pace yourself. By that I mean being active and working with your labor for an hour or two and then laying down to rest or sleep for 30 minutes to an hour.
Change the energy. Long labors require stamina, endurance and sometimes a breath of fresh air. You can go for a walk, talk to someone on the phone, take a bath or shower, write a letter to your baby, anything that builds you up, nurtures your soul and gives you a change of pace.
Long labors are not unusual, and do not mean something is wrong. Unmedicated labor has its own pacing and for the vast majority of births, it's not a lickety-split pace. Being prepared for a long labor will pay off for you if your labor is like the majority of labors, and if it is fast you can still pull from the preparations you have made to get you through with plenty in the tank at the end.