For bottoms that started out super tight. What was the best way you found to train your ass to be more receptive? I'd love to be more ready to go when bottoming rather than having to work up to it for a long time.
The most important thing for you is to be really relaxed and for your partner to take it slow at the beginning.
Secondly, have a regular sex schedule (which is not so easy to have) but you can help yourself with toys. My life changed when I bought my first dildo and experienced slow and long type of anal "fun".
As a boy I was really skinny and therefore my whole build was pretty tight so sex was also very painful because of that, and even using dildo to widen my anus I still had some troubles with bottoming.
Your partner, especially if you're younger, should be okay with taking it slow at the beginning. It wasn't before I moved in together with my BF that I could have sex without some kind of pain when he entered me just because we do it more regularly now when we have our own place and privacy.
Your "hole" is in theory just another body muscle and if you want it to be loose, you gotta make it and keep it that way. Also, try with butt plugs if wearing one is possible. They will make you more horny and loose your hole even more.