Although you'll find most of the time that we will mention three or four social media platforms please realize that there are hundreds that you could choose from and it's your responsibility to find the ones that best fit your audience.
It's important to have a well-rounded set of goals when using social media, especially in the beginning. For example a lot of people have an unreal and an unspoken expectation to use social media in the beginning and generate a ton of traffic. Although this is possible, it is not likely and I want to give you an example to compare.
I've said this before but rather than think of social media as a billboard, think of it as a building. A lot of planning goes into place when constructing a building for business. You look for prime location, what side of the street how many people pass this area on a daily basis, how much is it going to cost, etc.?