If you want to do the right thing then there are no short cuts, you must analyze real crew composition and production rates.

Fortunately in most construction jobs crew compositions are kept at the same level and assigned to many activities,  you do not change crew compositions for every new activity. Duration of activities will be a function of the quantity of assigned resources and volume of work. Therefore by creating multi-resources you can assign them to activities at a single click of the mouse. Activity durations must be verified one by one. 

I suppose if you are using capable software then you can select a multi-resource and click on the assignments tab then by selecting all activities the multi-resource is to be assigned you will assign all at a final single click of the mouse. This is more efficient than going activity by activity. Of course after all resource loading is done then you must double check activities one by one, sorry there are no magical shortcuts. Another trick is to use filters so that when selecting the activities only filtered activities are displayed for selection.

Another thing I do is I use skills as a resource instead of using specific trades. Foe example I use concrete formwork crew resource instead of the different trades such as carpenters, carpenter helper, unskilled labor ... I consider manhours too little  detail while specific trades (not to mention named resources) as too much.

Good luck.