Definitely agree with SEOpub on this one. It makes absolutely no sense to target a low number of keywords, ESPECIALLY if you are a beginner. If you're a beginner you don't know how to properly promote content, get shares, or build backlinks. In fact you probably wouldn't know a solid SEO service if it slapped you in the face, nor a crap service for that matter.
So in retrospect, you would want to target as many keywords as possible, and produce as much content as possible. AND NEVER target longtails that are 3 words or higher. If you do be vary weary of the fact that your preferred keyword density changes drastically and from what we are seeing, 0.4% is showing traits of being over optimized when utilizing longtails that are 3 words+. So literally using a long tail 1 time is about all you want to do. Google knows that typically you do not naturally see a 3 word longtail together more then 0.2% of the content.
My advice is to let the long tails come naturally. Throw in ONE longtail you want to target, here and there. Get a rank tracker and ke track of your keywords. If you're not tracking your keywords then just shoot yourself in both feet and keep walking. You're not gonna get anywhere. In fact thats like being footless and blind.
Keep producing quality content around your focus keyword, utilizing LSI to give your target keyword value.