Keep headers/logos under 125 pixels high. It takes up valuable viewing space, especially for laptop users, that is best left for the good stuff to appear"above the fold." Take a cue from the big companies, simple logos done well say it all. This is our #1 pet peeve - screaming logos and headers!
The secure your wordpress website Codex has an outline of what permissions are acceptable. Directory and file permissions can be changed either through an FTP client or within the administrative page from the web host.
Hackers do not have the power when you got these lined go to my blog up for your own security to come to your WordPress blog. You can have a secure WordPress account that provides big bucks from affiliate marketing to you.
Keep your WordPress Setup to date - One of the simplest and most valuable tasks you can do yourself is to ensure that your WordPress installation is updated. WordPress provides you a notice website here on your dashboard, so there is really no reason.
Black and whitelists phrases based on which field they look inside, in a page request. (unknown/numeric parameters vs. known post bodies, comment bodies, etc.).
Do your homework and some hunting, but if you're pressed for time and need to get this done once and for all, try the WordPress safety plugin that I use. It is a relief to know that my website (and company!) are secure.