A Sales Engineer is fundamentally responsible for the technical aspects of a sale, in my opinion. That means listening closely to customers so you understand their problems, presenting how your companies technologies fit the general case and presenting solutions to the customers specific challenges. It's a collaborative team game and specifically involves working closely in partnership with a sales person/s.
Communications, both verbal and written are the core skills. Take listening to clients - it means interpreting what they're saying and converting it into recognisable requirements, since many clients won't know the technologies or constraints in the way the specialist does.
The first thing you have to know is whether you'll enjoy the role, and be any good at it. While much of the role is about active listening, it also involves communicating complex technologies in a straightforward manner - if you enjoy doing that, then you may well enjoy the role. I'd suggest (if you don't already) presenting at conferences, writing blog posts and teaching other people are all things that you can do to discover if you'd enjoy it.
In terms of transitioning, I would look for situations or roles where you can work in a customer-facing situation. The closer you can get to sales and marketing the better. Your current organisation might be willing to work with you on it as part of a career plan: that's how I've handled people who wanted to move from back-end roles to a front-end one. For example, meeting with customers to update them on new upcoming technologies, or present how existing solutions could be improved, presenting at marketing events. If not in your current environment, then roles such as developer relations may be a useful stop-over point. Of course, the easiest way to transition is to .... apply lots ;-)
I should mention, that while the money is often good, there is a significant level of pressure. In most organisations the sales function is less stable with constant pressure to hit targets. While there will be fun if everything is going well, it's less so when it's not! If your sales person/team is having a hard time hitting their targets you will know all about it, and may suffer the consequences. You may also find that the obviously "technically right" solution is not as easy to determine when dealing with customers and sales people - both are an interesting design constraint. Finally, working with sales people is it's own challenge as they are often very different to technical people.
