Yes, definitely think about what you're wishing for before you wish for it! There is nothing easy about having twins, and I honestly cannot imagine *trying* for twins. Especially for someone who practicies AP, twins can make things really difficult: imagine trying to sling TWO babies all the time, cosleeping with two babies, nursing two babies and toddlers on demand, washing twice as many cloth diapers, etc. The hardest part for me is the emotional aspect. I cannot help but feeling like I am failing my children in some way because I CANNOT meet their needs all the time. I cannot always respond immediately to their cries. I feel like all multiples really miss out on getting that one-on-one time that babies are really meant to have. Also, twins can be really hard on a marriage. A really significant precentage of parents of multiples break up before the multiples are two years old. Twins are also really hard on any older children in the family.
I love my children, I love that they have each other, they are VERY cute together, but I would NEVER wish twins on myself or anyone else. I've recently started sending my guys to a home daycare one day a week, one at a time (they switch off who goes which week). So, once a week, for three hours, I have a single child. The first time it happened, I was close to tears the whole time. Everything was so easy and so lovely. I could really pay attention to my son. I could really get to know him in a whole different way. I could let him walk down the street, holding my hand. We could go out to lunch at a little cafe. I could carry on a conversation with him without any interruptions. When he asked to be carried, I could carry him. It was the best treat in the world. I felt like I could finally parent the way I'd always wanted to.
I don't think there's anything short of fertility drugs that you could really do to increase your chances of having twins, but even if there WERE, I hope you'd really think about the reality of what having twins would be like (not just the cuteness factor) before you did it.