New rule
I'm starting to impose a new rule for myself. The "don't buy more then enough of an item to level a skill.
For example if I wanted to lv prayer I should not buy more then enough to get me a single level. As I have this tendency to not stick with long term goals =p
It also places less of a burden on me to complete something.
Of course this rule is void if it is clear that the market is going to raise greatly and would be foolish not to get now.