Greetings Judy:
As I've stated many times, I am an advocate for dormant season pruning--whether the tree is a conifer or a hardwood.
Aesthetic pruning to facilitate mowing is certainly acceptable as long as you do not remove too many branches--again, I would wait to prune until the dormant season (i.e., late fall through late winter). The best way to prune a tree is a via a pruning saw--not a chainsaw!!!
Here are several good publications to help you get started with your pruning project:
http://www.na.fs.fed.us/spfo/pubs/howtos/ht_prune/prun001.htm
http://www.cals.uidaho.edu/edComm/pdf/bul/bul0644.pdf
http://mdc4.mdc.mo.gov/Documents/317.pdf
Best of luck!