Previously I used distemper on my wall. Can I use emulsions (for ex: tractor emulsion or premium emulsion) now or do I have to only use distempers?
The only distemper I'm familiar is a lime distemper, white wash, so I'm not an expert. But, a good latex or acrylic coating will easily out perform any cheap finish. If you have access to this type of finish then use it. This could be the premium emulsion. We use the term 'paint' but I think emulsion is the same thing.
It is possible that a primer should be used. It depends on exactly what is on your walls now and what finish you want to use. A good rule is when in doubt always use a primer.