The first one is to just buy domain names, without building a website and then reselling them. The second strategy, as you can guess from the first one is to buy a domain name, build a website, if needed you can even marketing and monetize it before you sell it for some profit.
That profit can be very satisfying, the reason is that many domain name buyers want to purchase a domain with already existing website that has Google rankings, page indexed by the search engine, backlights and so on.
As you know, you need to have the web development/SEO/copywriting skills and you must be willing to put aside some time and effort into developing the website and monetizing the domain name. If you lack the skills and time you can still make a profit from flipping the domain names without websites.
The key to you success is in the constant finding of domain names at a bargain and the constant finding of users that want to buy your domain names.
Here are some tips that might come in handy.
The first one is to choose a niche in which you have confidence and knowledge. The better you are the more success you are going to have with finding and selling the domain names. Everyone has a hobby or something he enjoys doing and is good at it so using that will give you an advantage.
The second tip is, use any tools you can find to speed up the domain name search process. Using the money you have earned on tools that find keyword domain names, domain names with type in traffic, auction domain names with page rank and many more won`t be a bad investment.
Finally the last tip is that you need to be constantly learning all that you can. Flipping domain names can have a huge payoff if you are willing to work hard and learn new things that will help you be better than the others.