Master the basics; fitness, nav, fieldcraft, weapon/shooting skills. Ultimately you’re going to Sandhurst where if you’re good at the above you can concentrate on what matters like the leadership etc.
Have a drink, but not too many; those drunken troop night out photos will be used against you.
Be careful with personal relationships; best avoided unless they really are ‘the one’ etc etc.
Be a grafter; get stuck in to mix concrete, carry a spare barrel or lug a piece of comms kit around, whatever the particular role/trade your unit is. Be known as someone who’s not afraid to get their hands dirty or shy away from hard work. Also your role as an Officer will be to step back and supervise, so take the opportunity to get stuck into whatever trade it is whilst you can.
Particular to the AR is to learn from your fellow soldiers why it is they joined, attend and what they want out of the AR. If they joined for a ski trip and there’s not been one for 5 years, make that happen. Conversely soldiers may just want a challenging, well run trade skills weekend.
Just a few reflections on my own experience. Don’t overthink it!