Write him a letter, and tell him you are looking forward to him coming to the parish.
When he gets there, be sure to introduce yourself after his first Mass there.
Be sure to go to his installation Mass, if your diocese does them.
Give him a card at his welcome reception, and let him know he can count on you if he needs anything.
Invite him over for dinner sometime shortly after he moves there (and try to do that fairly regularly).
Always take time after Mass to talk to him some (even if just to say “hello”).
After several months or so have gone by, make it a point to tell him you are glad he came to your parish.
It can be very difficult for a new pastor (especially someone young) to be in a parish that had the same pastor for so many years. When no one in the parish under 40 even remembers any other pastor, it’s hard for people to get used to a new face, a new voice, a new personality, and a new style- and their expectations are often VERY high. When you are constantly being compared to the previous pastor, it can be discouraging.