One space after the period or two spaces? This is one of the more hotly—and tediously—debated issues in writerly circles. (Another is the serial comma.) I’m a one-spacer myself. That’s Chicago Manual of Style dictum, and I have been doing it ever since I read The Mac is Not a Typewriter 25 years ago.
In Slate, Farhad Manjoo explains why you should never use two spaces. But I’m not all that rabid about it. Two spaces just seems silly to me, but certainly not worth arguing about. I have never heard of a manuscript being rejected because it contained too many spaces after a period.
Before publication, your manuscript will likely be loaded into a software program other than the one you used to write it anyway, and your work will be reformatted to meet the publication’s specs. So if you want to hang onto your two spaces, just be consistent so you won’t drive your editor or designer stark raving mad when she makes the necessary changes. If you want to join the one-space crowd, but find it difficult, you can rig Word’s “AutoCorrect” function to fix your spacing for you as you type.