Beijing to Xian and then back to Beijing

Hi there
My boyfriend and I are arriving in Beijing on 7 July and from there we are immediately heading to XA. We will not be staying in beijing so we do not have a hotel that the train ticket can be sent to. How do we get around this? Can the tickets be reserved and we pick up from the train station?

I understand tickets cant be booked too early in advance, our travels begin on 10th June so we will be on the road. We just want to know the best way to reserve train tickets so that we do not miss out. Our itinerary depends on this!

The trains we are interested in taking are G659 and T8.