Everyone is different with what will help them feel better. For me, a healthy diet with some specific changes and yoga are what I have found help me the most.
Specific diet changes include going gluten free (there has been research to support this in endo patients- http://endocomprehensive.blogspot.com/2014/03/gluten-free-and-endo.html), eating food as close to nature as possible/least processed, avoiding my trigger foods (lactose, gluten, cruciferous veggies, etc- see the FODMAPs diet for IBS), and reducing sugary foods/bad carbs.
I also found the following items the most helpful to include in my diet:
Plenty of clear fresh water. Add in some lemon. Spring water seems to help the most, but I have a water filter too.
Blueberries (probably any berry would be good)
Spinach. I don't whether it's the iron, the magnesium, or what, but organic spinach helps.
Albacore tuna. I've gotten some great deals on sustainably caught, low mercury canned tuna. Perhaps the omega-3's that help?
Egg white protein powder. I make a smoothie with this and spinach and I can tell I feel better. I have wondered if the l glutamine helps my gut. I can tell a difference between the egg white versus the whey.
I think the extra B vitamins and perhaps the low dose of vitex in this drink mix help. I drink it in the morning in my green tea.
Again, eating organic whenever possible, seems to help.
Again, these are things that have helped me and are not recommendations for what will work with anyone else. I can't say it made my endometriosis better, but it did help my health overall and improve my ability to deal with my endo and its ramifications.
PS Here's a link to some of the yoga poses I find most helpful to me: http://endocomprehensive.blogspot.com/2014/07/my-current-yoga-poses-that-help.html