I am struggling to get an even layer of paint on a ceiling. Any advise

Not sure of your details but, did you "seal" the ceiling first with something like Kilz so, the ceiling would not absorb paint? Also not sure what you are actually dealing with...paint soaking in, going from dark to light, buying inexpensive paint, improper painting techniques...anyway, hope this is helpful and good luck.

have you primed the ceiling?

How many coats of paint have you applied to the ceiling? Going from dark to light is going to take at least 2 coats--and possibly three. Let the paint dry well in between coats.

Thanks. 2 coats. I will add another.

you have to prime the ceiling first, allow to dry and then paint

It is ALL fixable, depends on patience and budget. Personally, I would go buy a gallon of Kilz and using a roller, go over the entire surface to seal any open "porousness" in the ceiling.

Since Kilz is white, it will also bring you to a lighter color to then paint the color you want. I say a gallon but, it may take more based on your ceiling size, you may need more. Roll slowly and keep the roller loaded with Kilz.

Don't forget that "W" motion when rolling.

I would also use the water based Kilz not, the oil based. Oil based actually works a little better but, is a lot more stinky (technical term I learn from my sister) and takes longer to dry.

Good luck!!!