Depending on the program, you can usually enlarge the text size of what you're printing in the same general manner. Whether you're printing an e-mail you want to keep or a document you've been working on in MS Word, you can change the text size with just a couple easy steps.
Open the document or email you want to print and highlight the entire text. You can either hit Ctrl + A to select it all, you can go to the Edit menu, Select All choice or you can drag your mouse over all of the text to highlight it. Once you have it selected, use the drop down menu, usually under "Format" and choose a bigger font size.
Most programs start out with size 10 or 12, so you may want to bump yours up to 14 or 18. You can usually go up to 36 or even 72, depending on how big you want it.
Once you have the text size changed, either hit Control+P or go to File, Print and print the document as you normally would.