This is actually a more complicated Q than you might imagine because there are various options and lots of gray areas in between. And always the answer is "it depends" because the best option varies based on your market, your skill set and who's giving the advice. (And what they are trying to sell you.)
1st off yes long tails are suggested because they are cheaper typically. When you talk about $7 per click, lots were even charged $10 per click. Those were Google slaps for people who had really low quality scores.
There are people that say to bid on a ton of low cost long tails and they add up. But in my experience that does not work - at least not in my market. I just don't get any clicks on the long tails and get all my clicks on my main KW.
But I imagine in other markets long tails work. Like in dating for instance there are probably a ton of viable long tail combinations I imagine.
I would NEVER recommend a newbie target broad competitive phrases like "Weight Loss" or "Lose Weight." That's just a crazy way to loose a bunch of money. I don't think most of the pros even go that broad.
I suggest for starters put your primary KWs in adgroups and keep your long tails in separate groups - don't mix long tails in with your main KW.
One thing that's certain, is you need to take the best advice and then test, tweak and test some more.