The groundwork a yearling should have before any further training begins is not a long list, but each item on it needs to be genuinely solid rather than marginally present. A yearling that has these fundamentals established is ready to build on them productively; one that is missing them will show those gaps at every subsequent stage of training as resistance, confusion, or fear that has to be remediated before real progress can happen.
The first and most foundational requirement is reliable leading — the yearling walks off immediately from light halter pressure, maintains pace with the handler without crowding or dragging, stops softly when the handler stops, and can be led past distractions and through gates without pulling away or running over the person leading. Leading is the communication platform that all other groundwork builds on, and a horse that doesn't lead well genuinely is not ready for more advanced work.
Beyond leading, a yearling should stand quietly for grooming and handling across its entire body, pick up all four feet on request and hold them patiently, stand tied without pulling back, accept being approached from both sides and from behind without alarm, and load into a trailer without a major battle. These are not advanced skills — they are the baseline that any horse intended for further use needs to have.
Yielding the hindquarters and the forehand from light pressure on the halter are also important pre-training skills because they give the handler tools for controlling the horse's feet from the ground — tools that become essential when the horse becomes more challenging to handle as it grows stronger and more opinionated through the yearling and two-year-old years.