What's the most important thing the military should do while going through this downsizing period?

Defend the Constitution of the United States of America from terrorism both foreign and DOMESTIC no matter the cost.

Move all landing craft from the navy to the army, and integrate it into the 7th Trans, which can then better train with the marines and army combat arms. Distinctive rank insignias can be worn by pilots and flight crew, or by marines. There would be a cost to integrate the forces, but the overall savings would exceed the cost in a short amount of time. The biggest saving would be in the cost to administrate a large service, since it effectively would reduce the overhead by creating one system to maintain. The number support MOSes reduced and consolidated would be shifted to combat arms, which would then increase the flexibility and strength of deployments. The service academies would still function, as the AFA would work in conjunction with WP to produce officers.

Im not saying get rid of recruiter but they should cut out all advertising for recruiting. Also lower the recruiting quota. That would add a large amount to the budget to all branches and lower the amount of people joining. If people want to join they can seek out a recruiter. By getting rid of service members that have experience and time in they are loosing great leaders and lowering our ability to be prepared for future conflicts.

The most important aspect won't be done - reintegrating the forces. There are a lot of duplicate services and specialties which bloat payroll and program budgets. For example: personnel, finance, medical, culinary, pilots, mechanics, and various support staff, should all be under the DoD (or US Armed Forces), while under that there should only be two branches - army and navy. Incorporate the Marines into the Army as a SpecOp branch, like the rangers. Let them keep a distinctive dress uniform, and BDU/ACU headgear. A specialized school and naval deployment keeps their traditions, but integrates their supply chain into the army's which reduces duplication and expenses. The air force simply melts back into the fold, which provides a brigade or division increased support and mobility while again, reducing costs and duplication. 

Get rid of marginal in all NCOES schools and in force the PT standards so that the out of shape soldiers are put on hold while the other to standard soldiers can advance and lead.

the military can grant early outs for those that want out sooner. prior to that, have classes on transitioning back to civilian life such as: writing a resume, interview techniques, finding a job (not guaranteed)!!

keep up your training listen to your neighbors  about the truth not the  the obumer  propaganda  , as he is trying to split this country,   bad things a comming  get ready  to defend America,from the muslim brotherhood,be safe

Build an esprit de corps in all services the like of which we've never seen.

Make Shure all contracts are honored as they were written at time of Induction.  Fallow through with what is promised at that time!!!