The secret for a glove-tight fit for trim corners is a coped joint. With this technique you can even make complex crown moldings fit without leaving gaps. http://www.familyhandyman.com/carpentry/trim-carpentry/how-to-cope-joints/view-all
Last week I posted that my husband and I were embarking on a huge weekend insulation DIY for the Fourth. Thanks to all the great comments and advice we got from everyone in the Apartment Therapy community, we were able to narrow down our insulation options and gain a general idea of their installation parameters.
Don't let your conditioned air literally fly out the gaps in windows and doors. Make this the month you finally seal up those doors and windows with new caulking and weatherstripping. The project will literally pay for itself this summer.