Unfortunately, screamers, flamers, and burning chariots are downright awful for their points. They are all way too fragile, and have immense trouble getting damage to stick.
My recommendations:
Swap a herald for either The Changeling or Blue Scribes, both are pretty solid (though the former is more situational). You will probably want to get both eventually.
Fit in some units of Blue and brimstone horrors. They are immensely cheap, and can hold objectives, and protect your more important units from close combat with ease.
Look into the Changehost Battalion. Its tricky to master, but great fun and very powerful is used right.
There is a massive thread discussing Disciples very in depth here:
http://www.tga.community/forums/topic/5998-lets-chat-disciples-of-tzeentch/