Just going straight to rear without tap can be good for tech natural where its a bumpy downhill run-up to a overhung rock, takes some of the risk out as timing doesn't have to be bang on. Also good if theres a dip infront of the rock you wanna get up, can just air over it without worrying where your front wheel is.
Bit fiddly and time consuming, but you can get the file in horizontally resting on the lip you want to file (below the tyre bead lip) and file down till its gone, then move round and carry on. Best to get as much out with the grinder as you can.
Take wheel out, take tyre and tube off, get grinder out, grind out inner wall.
Thats the basics of it, are there any specifics you want? Ask if there are