Your question is a bit vague. Are you asking what a good niche to get into is? If you are, I think it is safe to say if you are just starting out getting into something you are passionate it about and are very knowledgeable in.
Actually, I said I am thinking in starting a website aimed at helping others do their link-building tasks properly. Think of it like an online manual. My question is aimed at making a list of topics to cover on the site. Thanks.