In RSC, I'm a bit of a noob (only 30 combat and 50 mining) and was wondering where the best coal mining spots are for noobs like me. I have already tried mining at the Barbarian Village and Lumbridge Swamp, but I was wondering if there are any better spots.

Stick to Lumbridge Swamps, it is close to Draynor Bank and you are in no real danger.

Bring the best weapon you can use + best chest you can wear. Bring your pickaxe and go to the wilderness coal mine north west of edgeville (level 9 wildy). There's 20+ coal rocks to mine, and the only thing attacking you will be level 25 skeletons. There are places you can hide so you will rarely get attacked while mining. If you have food in the bank, you can just heal after each full inventory, and there's also a bed right next to the bank for quick sleeping.