It’s great to hear that you are growing your own Christmas tree and they do respond surprisingly well if the growing tips are snipped back regularly in late summer or autumn. Remove any upward growing stems that compete with the leader and trim back any wayward shoots to maintain a nice even shape all round. Any dead or damaged shoots should also be removed. The main point to remember is that you should not prune back further than the current year’s growth as new growth will not emerge from old wood.
If you are growing your tree in a container then it is also important to keep it well fed and watered. If it is becoming too large for its pot then you will need to repot it using John Innes No. 2. compost. Unfortunately they are not particularly well suited to growing in pots long-term and may start to struggle as they mature.