The greatest way to ensure a capable of force is to enable and provide training or education in areas both within a legionnaire's scope of responsibilities, and within their own personal interests.

That's the first part.
The second part is making it as little of a pain in the ass as possible.

Let's reach into the errors of others to pull some wisdom from their failures.
You're a soldier in the Unified Empires infantry, and you'd like to learn how to be a squad machinegunner. You go to your NCO and ask how to go make that happen. First you'll need to send a request to the schoolhouse over at another base that handles machinegun training, to see if they have any open slots for the next training cycle, or maybe the cycle after that in the next three or so months.
They send back that they've got an open slot for the next cycle and your NCO sends in the paperwork they need.
All in all, a good process so far.

The next day, your NCO says that the unit's SNCO has to approve your training as well. You die inside as your unit's SNCO takes days to get to anything, but after two weeks of constant reminders and harassment, the SNCO approves the training. Your NCO gives you the forms you need, you get your flight set up through your base's travel office, and you're due for departure by next week.

You're in the middle of packing your bags the day before you leave when your NCO sends you a message. The base CO wants to do a field exercise starting in three days, and wants full participation from all units. Your unit came up as red in the readiness tracker due to three people being away during that time, including you.

Your SNCO explains that there are two soldiers on paternal leave for the next three weeks, and one that's due to be away for training. The base CO doesn't care what the reasons are, the readiness tracker is red. It needs to be green, not red, make it green and make it green right this instant. After a half hour rant on the importance of readiness for a war fighting force, how soldiers know what they signed up for, and that any red trackers will make the base CO look bad in front of some general, your SNCO is ordered to pull everyone back to base within the day.

As an aside, having served as the aide to a general officer in a past life, I can assure you that the hypothetical general couldn't care less about any red trackers for a base in some flyover territory.

All of this to say, your training request has been cancelled and you now need to get a new packing list for the upcoming FTX. You also need to go back to the travel office and get your flights cancelled, fill out the paperwork there, fill out the cancellation paperwork for the schoolhouse's records, and so on. Two days later you're in the field, covered in mud after rucking in a circle for a few hours, wondering if that water you got from the buffalo is gonna be part of your future cancer claim, and sitting out in the open doing dick all for about eight days before everyone heads back to base.

Before you can even unload the trucks or get a shower the base CO orders an all call formation, and you contemplate locking your knees to get out of it sooner. You spend an hour getting everyone in place before the CO shows up and spends the next hour extoling the value of maintaining readiness, good order and discipline. He goes on to say that you all need to stay alert, be prepared, and ready to go at a moment's notice, and then runs off on a tangent for about another half hour before everyone is dismissed.
No, the base CO did not participate in the FTX whatsoever.

A week later you approach your NCO about the training again. You do all the same steps as before, you get an available slot for the next training cycle in three months, your SNCO approves of it after hunting him down, you make doubly sure it's good to go by clearing it with the unit's CO, and you proceed to wait.
Four days before your departure, your NCO pops in to tell you there's been an issue.

Admin at the schoolhouse base lost the paperwork for your training cycle, you'll need to redo the entire process. Due to numerous reasons you'll also have to go to finance and pay for the flight, then file for reimbursement three months from now.

You give up on the training and feel rightly justified in skating for the rest of your enlistment.

A long-winded example, but it shows numerous areas where guardrails need to be in place to make the process of training/education as bulletproof as possible. That anyone should even try to better themselves in their field, or just in general, should be encouraged but also protected at every possible level.
For GDS, we work towards that goal by adhering to the following:

• Training/education approvals require two people: the legionnaire, and their commanding officer. Any issues that come up due to the legionnaire needing to go on a TDY or take leave for the training/education is on their commanding officer to handle. That is their role, and the legionnaire's is to focus on their training/education.

• Finance covers all costs related to training, required equipment, travel, lodging, meals, and other necessary expenses for the duration of the training/education. These services should all be handled in-house; however, they will also be covered in other instances where that's not possible. If justification is required for certain expenses, this is handled by the legionnaire's commanding officer.

o The paperwork for all of this is filed by the legionnaire and their commanding officer and is three pages maximum. If reimbursement is required, the process is mandated to take no more than 24 hours by regulation. We don't need legionnaires waiting 4+ months only to be told now they're the ones that owe money.

• Legionnaires in the midst of training/education are placed in a "hold" status regarding orders. This means that they cannot have their training interrupted by sudden last second orders. That is a problem for their squadron, commander, or base to figure out.
The only ones who can override this are the Arbiters, and it must be a unanimous decision. This has happened only twice:

o A Fortress had its DFD system and all backups go down after being hit by a severe storm, requiring a lead engineer to be called back to assist with repairs, as well as fixing the redundancy issues.

o An incident that I cannot disclose the details of, but it involved a warhead, a misconfigured signal chain, and an incredibly uncharitable time limit.

• Lastly, legionnaires that further their education in their job roles whether it be through classroom learning or hands on training, are paid up to 20% more once their training is complete. The average is a 10% increase, and this is often after taking classes or training that lasts around three or four weeks.

The final point there is often the most crucial one. We can do our best to ensure a legionnaire receives training, but it means jack all nothing if they aren't being properly compensated for their effort and drive to better themselves. This can become prohibitively expensive when multiplied across an entire PMC, and as such we put extensive work into ensuring our finances can handle large expenditure surges.
I've found that early on, we had to more or less beat the phrase "That's how a job works" out of officers and NCOs. It'd become customary to tell subordinates that overextending themselves and going beyond their job role was expected, and done for "the good of the company" rather than something as selfish as expecting proper compensation.

That's a problem we ensure doesn't happen here.
Good pay means less stress, less stress equals more energy to become better, becoming better benefits us all.

Strive to become a become a better person, and we'll be behind you the whole way.

-FrW Hansuke Ito