I was wondering what meditation type is most conducive to improvement of mood or even mood stability in Buddhism? I noticed that most of my problematic behaviours and attitudes depend on low mood.
According to my teacher, mood instability comes from not having a stable frame of reference as far as one's values. Meaning, when one has a stable system of coordinates in one's head, according to which everything is evaluated, one's values are stable and one can optimize one's actions within that frame of reference. However, when one does not have that, then for such person it is typical to waver between different coordinate systems of other people. As a result, one's values keep fluctuating. Today, according to this system, everything is great - and tomorrow, according to another system - you are a loser.
The traditional medicine from that is to work on internalizing the Dharma until it becomes one's stable frame of reference. This starts with taking Refuge as the commitment to never hold any other system of values higher than Buddha-Dharma. As a result one's values and one's assessment of one's situations stabilizes and the mood swings diminish and disappear.
The next step is to work on going beyond a single frame of reference and to become capable of switching frames of reference without getting stuck mentally or emotionally. This ultimate level of this is cultivation of spontaneity, or being oneself. This basically means that one becomes one's own system of coordinates, one always trusts one's own judgement and therefore is immune to any and all mood fluctuations.
In terms of meditation, I would recommend analytical meditation on the first three Noble Truths.
You could take a satipatthana approach by noticing the shifting mind states throughout the day. If one does this with such diligence and discipline you will eventually notice that all the shifting mind states cannot possibly make up you as a person. This brings forth knowledge of...
impermanence: they're always changing.
suffering: wanting or not wanting
leading to the partial or the full realisation of not-self.
You will have to 'know' many times by patiently observing your own mind states.
One will also gain insight into the four noble truths along the way by seeing how you are creating your own suffering. Once you see this, you're on the path.