I'm full of bad habits but I'm fine with them as I'm relatively new to betting on horses and I'm doing it for minimal amounts and for fun.
I'll find a meet, usually in Ireland, and bet on pretty much every race of the day (except the bumper.) If I'm up early, or awake all night, and have my picks selected before any horse has withdrawn, and a horse of mine does withdraw, I'll usually find another, even if it means picking a horse I had dismissed previously.
Like I said, I'm relatively new at horses. Despite having a RacingTV subscription for a year, and watching Cheltenham for three years (I don't count being nine years old and betting at Point to Points, even though it's very much part of my childhood,) I'm very infrequent and go in bursts of looking at races. I don't know what I'm good at picking i.e. which types of races, and sort of justifying betting on everything in a day by saying I'm figuring out what my niche is.
I'm heavily reliant on my Best Odds Guarantee. I don't have the nerve (or knowledge) to wait for what I think might be a better price coming up. My horses often reach higher prices I could have waited for, but I don't know when to quite jump on a price, know when a horse is being backed from elsewhere, or when they're going to drift. In the same vein I have absolutely no insider knowledge, no contacts, and am almost entirely relying on what I've seen before or what I read off a quick read of the Racing Post form guide. On the "what I've seen before" a horse I think is good, that doesn't perform, I can be quick to dismiss, even if I get the feeling there's a possibility they can pull something out. (Nazine today in Ballinrobe was a super impressive maiden winner, but I saw them do poorly, so I have no inclination to to "test" my "spirit" by backing them again today, even if viewing that maiden win says they can do something special.)
The final bad habit I can think of is how I judge an entire day of racing. A reason I use to pick a horse in the 2.40, to justify my selection, could be entirely dismissed in 4.10, despite all the same logic applying, I instead just go on a feeling.
I suppose a habit that's both good and bad is that I have absolutely zero trust for reported goings. I'm far more likely to look out the window, or look at what the weather was, and no matter the drainage, think, "There's no bloody way that's good-to-yielding."
Saying all this, outside of the grand national my biggest day of betting was Cheltenham three years ago, when I was putting at most €2 on each race. Since then I'm putting even less on horses, so for me it really is a day of watching races and risking minimal amounts. I'd like to be a winner, but if three years of sporadic horse racing betting has cost me, in bets, more than about €75 euros (not counting bets in the bookies in cash from the pub) I would be very surprised. What it's cost in booze and RacingTV subs is another matter. What it's given me in a day's activity and enjoyment is what it's about.