It depends on what shaped tree you are wanting to have once it is fully established..

Under canopy management in the BPR there are some good tips on training young trees with tip pruning or to a central leader – https://avocado.org.au/best-practice-resource/growing/canopy-management/training-young-trees/

There are various opinions on when to start these practices with most starting after 12-18 months after planting. I have heard the opinion that one should wait two flushes before pruning to ensure the root system is well established before pruning commences