Unfortunately it isn't easy for a number of reasons.
Responsible sites can label their site as containing "adult"
content inappropriate for minors, and perhaps something some adults
prefer not to stumble upon as well. This is what we have done using a simple, but clear and effective, method as proposed by Safelabeling.org or the similar one from RTALabel.org.
We want to do our part to enable those individuals who take offense to
porn to be able to avoid it, and of course minors, browsers at
inappropriate locales etc etc, to have the choice to stay away from
sites like ours.
You would think that all browser already understood this kind of
voluntary labeling and could, depending on user settings, filter the
Internet browsing accordingly. Sadly this isn't the case yet, but hopefully it will soon happen.
There are also other methods for a responsible webmaster to label his
content, but they are frequently overly complicated and not much more
effective, if at all.