Working on a blog creation website; should I be creating a new table for each blog, or keep everything on the same table?
More than a few thousand tables or databases is a bad idea in MySQL.  This because of MySQL's dependence on the filesystem, and most OS's can get bogged down when a directory has "too many" entries.

Hence, I vote for a single Blogs table.  You will probably need few other tables to round out the app.  Probably they will all be in a single database, but that does not matter much.