"Shorter is better" is not necessarily true. Within the supposed 65-character limit, you can often boost your overall SERPs by creating carefully researched "long tail" keyword titles. If that is an unfamiliar term, try Googling and researching long tail keywords. It can add some effectiveness to your SEO. EDIT: An illustration of that would be the title in my signature #4 below. The long tail title there allows me to score in the SERPs for both "insight for living" and "living by faith". That's the idea behind the long tail keyword concept.
If you are in a niche market that has keywords that does not have much competiton you can use longer titles cause title is one of the strongest parts of th pages , but if you are aiming highly competitive keywords you should make it short.
Yes, the long tail concept believe is good enough for your purpose, but in competitive SERPS I would focus on the main keywords for that page, maybe adding less important ones at the end, but not too many.
I didn't know the long tail concept. It seems very interesting. Now, I'm not in just one niche, I am in four niches that are entirely connected to each other, all in one website. What advise would you give me taking that into account? Thanks again.
It depends on how many pages you have per website, but I would focus on the keywords for each page, as I said already, making sure that each website covers, with the page titles of course, all keywords that you are aiming at. And stay under 55-65 characters, just to play safe, and most important keywords first in a readable way, that is user friendly and catchy enough. Good luck!