I'm an eBay addict and have been using it for years.
My best tips are to bid late, sort of in the last 25 or 30 seconds, and to place as high as you want to go. Don't bother bidding days early as then the price will go up and up so the end price will be high. Use a snipe tool,
www.justsnipe.co.uk is fantastic, I know BVH uses it also, and I always win every single auction with it.
For cages, it is best to look for ones local to you that you can pick up as they will be cheaper than the ones going for postage.
Always shop around also, and try different search strings since some items won't be listed obviously
Good luck!