A good place is here: http://forum.xda-developers.com/sprint-htc-one/development
Always a good idea to read the first few posts of a ROM thread for any install instructions and any special requirements (particular firmware versions needed for example). And back up everything first: both app and data backups (e.g. using Titanium Backup - make sure your contacts, messages etc. are backed-upp too) and a "nandroid" backup (i.e. a backup made using the custom recovery). These have different purposes: unless the ROM is very similar to the current one it's likely you'll have to do a factory reset during the install, which is why you need your current apps and data backed-up, so you can restore them afterwards. But if anything goes wrong with the ROM install you will want to restore your old setup, and that's what the nandroid backup is for. So I always do both before installing a new ROM.
Always a good idea to read the first few posts of a ROM thread for any install instructions and any special requirements (particular firmware versions needed for example). And back up everything first: both app and data backups (e.g. using Titanium Backup - make sure your contacts, messages etc. are backed-upp too) and a "nandroid" backup (i.e. a backup made using the custom recovery). These have different purposes: unless the ROM is very similar to the current one it's likely you'll have to do a factory reset during the install, which is why you need your current apps and data backed-up, so you can restore them afterwards. But if anything goes wrong with the ROM install you will want to restore your old setup, and that's what the nandroid backup is for. So I always do both before installing a new ROM.