Manali is a small town and most places can be covered on foot. For places farther away, hire a taxi or take local buses. Bargain with taxi drivers to get a better deal. Keep in mind that traffic can be heavy during peak tourist season.
If you have more time, consider adding a day trip to Rohtang Pass or a visit to the Naggar Castle. If you have less time, skip Solang Valley or Manu Temple.