First-time visitors often try to squeeze too much into Penzance, but the town rewards a calmer plan. You do not need to see everything to get a good sense of it.
Start with the town centre and Chapel Street, then move towards the harbour, the promenade and one or two bigger sights such as St Michael's Mount, Penlee House or Jubilee Pool depending on your interests. That gives you a proper feel for the place without rushing.
The aim is to leave with a sense of where the town sits in Mounts Bay and how the centre, harbour and coast all connect. That is the part of the visit people usually remember most.