Starting Out

I’ve recently discovered my desire to take things deep. I have my favorite toys that are pretty standard girth and range from 6-8” long, and a larger toy which is 8” in girth and 10” long, as well as a recently acquired double ended dildo that’s 18” long. I want to be able to take the 18” as much as possible, but can really only take about 8” MAX before things get uncomfortable/ hurt. I want to really start doing depth training, and am looking for advice on how best to do it.