Have you seen the new blog post from the Tuck adcom about recommenders? If not, check it out now. It answers a lot of frequently asked questions and gives some helpful advice. I've recently been asked by a couple of blog readers some similar questions, and I think Pat Harris (Tuck adcom) answers those questions well.
But anyway, if you've read that post and still want my advice, then keep reading. Once you've decided who to choose for your letters of recommendation, it's not enough to just send them the online link and leave the rest up to fate (well, it's probably enough for some people, but if you're reading this blog, then it shouldn't be enough for you). However, you absolutely can not (and should not) write your recommendations yourself. Nevertheless, you can provide guidance to your recommenders to steer them in the right direction.
I created individual Recommender Packets and set up coffee chats with each of my recommenders. During our meetings (and in the packets), I noted my career goals, explained why I wanted an MBA, and then reminded them of some of my major accomplishments (i.e. "Remember how awesome I am and all of those great things I did!") I don't know if they chose to describe those things in my letters of recommendation, but it was a helpful starting point to get them brainstorming. I also let them know about particular areas that would be helpful for them to address. For example, coming from a less traditional field, I needed the adcom to know that I do actually have strong analytical and quantitative skills, and I can really compete with the finance kids. I let my recommenders know that this was an area of concern for me, then I asked them to comment on some of the major initiatives that I've led that highlight those areas. Your recommendations should reinforce the strengths and stories highlighted throughout your application, while also providing additional insight into your candidacy.