Install Opera and/or FireFox. Install NoScript in FireFox.

Make sure (with shortcuts, etc.) that Opera/FireFox is easier to
start/find than Internet Explorer. Try to make Internet
Explorer unsusable, like directing it to a non-existing
proxy-server, etc.

Make Opera/FireFox the default browser.

The following makes use inconvenient, but the question was
about security:

Block JavaScript for all sites (e.g. set in Preferences in 
Opera and using NoScript in FireFox), except for the ones you 
explicitly allow. Most of these will need to be set later by the 
(inexperienced) user. This is where it becomes inconvenient.

Allow JavaScript for some common sites, e.g. YouTube and
Gmail. Test that it actually works.