There are some niches which are highly competitive, and if i do research using adwords, almost all keywords have 100% competition some who have little or 0 competition has only 1600 searches per month. how i can find keywords for such niches?
It is getting tough. You may have to be "very specific" in your targeting and build. Instead of going for "toasters" you might have to go for "brown toasters" or "big brown toasters" Though there may not be a lot of searches for these the guests that you do get are very targeted. After that you go for "small brown toasters". Keep repeating in variation until you have an inventory of small but specific sales pages (keywords) After some time you may find that you own all the keywords for toaster and everything related to it. That makes you an Authority to Google. Good Luck!