hey, im pretty experienced at deepthroating so i think i can help a little ?
some of the things i used when i was learning how to deepthroat were;
when i was going to brush my teeth i always brushed my tongue more deep inside in the place that usually "activates" your gag reflex
also when brushing my teeth i used to gently touch and rub my tonsils
do this while you try relaxing your mouth
also, gargling using water with a bit of salt helps a little
some other tips is training with specific positions, like laying on your back with your head down then using something like a dildo, this position helps a lot whatever you are using to slide in your throat easier
also, use a lot of your saliva (LOL i didnt see the date of the thread until i wrote all of this)