I would prefer to set Times New Roman 12 as the font with my email.

Sometimes...not always but sometimes....you will get a better answer if you provide some information. You didn't even bother to mention what email client you are using so I doubt anyone here is going to just randomly spout out the correct procedure without knowing what you are using.

Location of settings for Widnows Live email?

Try this:

On the Windows Live Mail tab, click Options and then click Mail.
On the Read tab, click Fonts.
In the Font size box, select Smallest, and then click OK.
Click OK to close the Options dialog box.