When we are talking Guard, I think the big issue is what the formations are within your state.  We have an IBCT, and other DRUs are a Troop Command, Regional Support Group, and then some smaller training type units.  Guys that branch MP, for instance, have almost nowhere to go after captain, where if you are combat arms you have almost unlimited potential, especially Infantry and Armor/Cav, of course then the limiting factor is the ability to move into the USAR and having to deal with O1A slots.  I found getting a functional area, in my case 57A Simulation Operations, is a way for me to balance out the needs of my brigade and my own career needs to provide the flexibility I require.  In my case I didn’t necessarily go for the selfish, but looked at where the unit needed trained personnel and actively made my case for the position, because I knew that sending me for a total of 26+ weeks of school (FA qual course plus associated ASIs for Red Team and Knowledge Management) would be an investment on their part.  In the end it worked out for everyone.

Having a mentor is of course a great resource, however look for more than one, especially given how political state and national levels get in the guard.  Know those that will tell it to you straight as well as who the power brokers are…unfortunately often not the same person.