Warmest welcome to TRF Robnant. I’m sure that’s echoed by everyone here too.
I agree with Librettist regards spotting over-priced horses and I think you can only really begin to do this by watching as many races as you can and therefore learning the profiles of individual horses/jockeys/trainers/tracks etc.
The ideal scenario to lay would be to know a horse (say a 10-1 shot) is going to travel really strongly throughout the race, and look the winner, but then for it to falter /not want to win in the final stages.
Therefore you could back it at 10s before the race before laying it off for a fraction of that price in running. Basically you’re trying to use your knowledge to develop a scenario by where you either break even or go into profit whatever the result.
I’m sure you knew that already but just keep watching as many races as you can and look for those who regularly start as favourites but usually finished placed. All-weather maidens for 3yos and over are usually a good place to start when laying odds on favourites.