Long-Tail Keywords – specific keywords usually with 3-7 individual words in a phrase. They are highly targeted and MUCH easier to rank for than broad keywords (all mine are long-tail). The lower your domain authority (check using OSE), the less competitive (more long-tail) your keywords should be. If you can get more specific and the keyword still shows up in Google Autocomplete, Moz Keyword Explorer and other keyword tools… choose the SPECIFIC one.
The amount of money you can make can depend greatly of you budget. If you have a small budget and you don´t have a lot of money, then you have to start with free marketing methods like article writing, blogging, forum marketing and such. It takes a lot more effort ant time to have success with these methods. But they are very effective if you keep writing articles and participate in forums. You can make $100 a day within just a few months just with article marketing.