Increasing likelyhood of twins for future pregnancy

Hi there! I was wondering if anyone knew of natural ways to increase the likelihood of twins. I am currently pregnant with my son (he is my first) at 27 +2. My husband and I are already planning for our entire family. We would love to have twins.

I've heard African Americans, tall women, overweight women, women over 45, and people with twins running in the family are more likely to conceive multiples, but if anyone knows of natural ways to increase the odds (so not IVF or fertility drugs) please drop a link in the comments. I will be waiting 18 months after my son is born to begin trying to conceive, I just want to be as prepared as I can be.

Please don't misunderstand me, life is an incredible gift and I will be happy even if we only have one child. If you have negative comments, please move your attention else where.