Start in the job position you want -- it'll be harder to get there later.
First Get Here
When you hiring negotiations, I've heard the invitation a few times -- to myself and to others -- "first get here, then we'll figure that out". If you're starting a job, instead get the position you want when you start. If you don't, it's less likely to even happen.
When you make a jump for a company, you want to go for concrete reasons, some that should materialize day 1, not for what might be. Always clouded the future is.
Control the Future
The best way to predict the future is to invent it. So invent it when you are negotiating a starting position.
Don't rely on a promise of something in the future. The person promising can't control it. It's unknown. He might like to. Even if that person is totally sincere, the future is still unknown and uncontrollable. There are so many factors that will fall outside his control.
There will be other people to convince. There will be internal interviews. The culture of the company is constantly changing. There will be new, different requirements invented by new, different people. There will be current commitments that need fulfilled before things change. There will a performance plans that need performed to before one is seen as ready. There will be intervening years and lesser positions.
(Now all this might be true anyway, depending on what you're aiming for and where you're at. You might not be able or want to bypass it. But if you're going to jump to a company for a certain position you have in mind, you will do yourself a favor if you can secure that position before jumping.)
If you put off building out a real implementation of your desired position, you risk a mismatch with the hiring manager or team -- just as if you rely on a design doc until late in the process to code it. If your design ends up not fitting the actual needs, you find out late, it's expensive, and you have to adjust, sometimes drastically.
So do the work to share a vision. Your mental picture of the job you want and will do is probably a lot different than your hiring manager's. Talk it through. Take time. Stay on the line. Ask for an extension. Work it out. It is hard to clearly share those thoughts and plan the future while in the dance of negotiating a new job opportunity, but you should try.
Time for Change
When you start a job, it is one of the times that the social expectation for you to even be negotiating is at its highest. Ideas about your responsibilities, you worth, your compensation, your title, your career path will all flow more freely during this time.
At a future moment, you'll be salaried, people will have become used to what you do, how you do it, what they're paying you, and the inertia of those things in practice will be a force against negotiation. That same conversation in a one on one meeting with your manager won't have the same power and timeliness as a starting negotiation.
Beneath Your Means
And if you do bypass this advice and "first get there", it's likely that you'll feel unfulfilled or slighted. You'll know that you had a higher or different vision for yourself that you're not living. That moment of not working it out beforehand will disturb you as a sign that you're doing less than your best work or living in a less-favorable reality than you might be.
So take time, share your vision, get the position you really want, or hold out for when and where you can really make it happen.
Do you agree? How do you help yourself start in the job position you really want?