Horses... Backing and laying

I've been messing around on here for a while now and eventually started to show a very small profit laying dogs here and there and betting on the odd footy match however the small profit I've made along with my entire bank on more than one occasion have been frittered away by backing or laying horses. I find myself looking at the recent form, thinking to myself that horse will surely win hands down... then backing something else or even laying it!? usually because its at a short price or whatever, it makes very little sense but i'm sure a few of you will be able to relate to what i'm doing, my question is... does anybody have any kind of advice (apart from the obvious 'stop being an idiot etc') on talking yourself into or out of a bet, for example weighing up the pros and cons of each bet, criticizing the bets your going to put on etc basically a bit of a selection system where you only place bets if the pro's outweigh the cons?