What common ingredients to look for/avoid in cats diet

I'm trying to research diets for my cats. I also feed several cats and kittens in my apartment complex that I believe were abandoned by past tenants. I am very concerned about their health. I see several loosing their hair and what looks like an infestation mange. I know I can't take care of every problem immediately but I can help them keep their immune system strong. Any dos and don'ts advice as to what I should feed them, would be helpful! I know some some ingredients that are found in cat food are not so good for our feline friends. On the other hand, I know some ingredients are. Thank you for your advice!!!

Well, if you have a flexible budget the best food possible would be homemade. I feed my outside cats a combination of homecooked with EZcomplete mixed with some decent lower quality wet food. Mostly FF pate (chicken and turkey) or sheba. You could also feed Friskies canned turkey and giblet, which comes in 12oz cans. I also give my outside cats probiotics mixed in their food AM and PM to help boost their immune system. I use nexabiotics. 

At the very least feeding wet food over kibble is the most ideal. Cats are obligate carnivores, so wet food that doesn't contain a lot of veggies or carby fillers is the best. 

If they have mange though you really need to trap them and control the infestation. You should also make sure they've all been spayed/neutered or you'll end up with them reproducing at rapid rates. 

the majority of ingredients in most brands of cat food are terrible. it's a bummer when you realize this. there are only a few brands, in my eyes that are decent to feed. BUT since they're neighborhood cats, I would think something not expensive would be the most likely option. Any wet food I'm sure would be welcomed. I knew a gal that bought walmart brand just for the outside kitties. I wouldn't feed my cats that but these are outside kitties, they probably catch mice & birds too.

Whatever your budget can afford, I'm sure they will appreciate the food.

Thank you for the advice!!

Maybe these articles will help you:

http://www.thecatsite.com/a/how-to-choose-the-right-food-for-your-cat

http://www.thecatsite.com/a/by-products-in-cat-food-5-facts-you-need-to-know

http://www.thecatsite.com/a/grain-free-cat-food-what-does-it-mean

http://www.thecatsite.com/a/what-makes-the-best-canned-cat-food

http://www.thecatsite.com/a/what-makes-the-best-dry-cat-food