I'll try to be as clear as i can, my english is bad and i'm sorry.

The most difficult part in playing ailment build is to find the right balance between Material and elemental (mostly).
Occult ailments are easily applicable, a lot of skills got runes as Curse, Weakness or even Stasis without converting any of your damage into the specific ailment.
Why i talked about converting damage, a lot of skills got runes that convert physical damage into "N" ailment. If your weapon ( or weaponS) does not have enough physical damage, you'll not be able to convert your damage.
Here an exemple i have a bow with physical and rend damage and i want to play with railgun (convert physical to lightning damage). If my rend damage in the skill detail is more important than my physical damage, railgun output will be rend and not lightning. Which solutions do you have ? you can put some physical damage on attacks on Offensive 1 gem or get a weapon with a lot of physical damage.
This example is true for every ailment, if your ailment damage becomes more important than the converted value you'll lose an ailment.

It's a real headache when it comes to put 7 ailments. I play like that and i have to put them in a specific order. I have to put lightning and stasis with railgun first, than bleed and poison with hailing arrow, than curse with dusk, fire with gaavanir and sacred each time i'm blocking. If i miss something in this list i lost either lightning (it becomes poison generally) or bleed and poison if i stack fire and curse first. I play pistol and 1H (pistol 83-255 physical 90-90 poison and 1H 101-210 physical 90-90 rend) i have enough physical damage to convert railgun into lightning instead of poison or rend and gaavnir in fire instead of poison and rend. Well i take my build as an exemple but i think it is more easy to understand.

First, check you have a lot of physical damage and put gems as you like into your weapon(S).
Second, convert your skill damage into specific ailment with the rune.
Third, try. If you lose ailments on skill, start again from 1 but remove your gems and put 1 physical + 2 ailment gems and try again until you find the right balance.

I hope i was clear XD if you don't understand something i'll try to be more "understandable".

EDIT : oh i forgot to precise, i have to put my ailment in a specific order because of Immortal Offering node ( which increase specific ailment dmg type by 5% (5stacks)) so if you play with it take care :).

Check out my little write-up. It's from before the last nerfs but the mechanics are the same. https://www.youtube.com/watch?v=c_DQxjrLuS0&feature=youtu.be.

I worked very hard on that video. I don't appreciate you trying to claim credit for it.

thanks. that helped me understand better