Thinking about myself is my default position. This may be alright for someone who really loves themselves, like Piers Morgan, but if you think you are nothing special then constantly thinking about yourself is probably not a good idea. Your self image might be unable to bear the weight of so much attention.
You have two ways to remedy this. First you can try to change the image you have of yourself and start loving yourself to bits. For this you might like to try positive thinking. However, go this way and you run the risk of self-deception and losing interest in others, who will then lose interest in you.
The other way is to spend less time thinking about yourself and more time looking at, and thinking about, other things. This way strikes me as being the better of the two.
So, spending my time thinking about anything that isn’t ‘me’ would probably be good for my mental health. We can of course argue over what constitutes ‘me’. Mystics claim that selves don’t exist so there is nothing for me to call ‘me’ or even ‘mine’: we are one with everything. At the other extreme are the megalomaniacs who think they are the whole world. These two extremes strike me as being remarkably similar; both posit a One rather than a multitude among which you find yourself. Occupying the sane middle ground are those who haggle over whether my liver function, my breathing, my wife and my house are part of ‘me’ or part of the outside world.
Personally I think arguing over what belongs on which side of the subject/object divide is a red herring. What matters is not how things actually are but how they seem. After all, we are talking here about psychological reality, not real reality. If you are convinced that your breathing is not part of you then by all means spend your time watching your breathing. And if on the other hand you find it hard to believe that your breathing is not a part of you then look at a glacier instead. That is definitely not you.
Wherever the subject/object divide lies, thinking less about yourself must surely be a good thing, both for the self-obsessed themselves and for those who have to spend time with them.