To edit your blacklist, navigate to My Account >> Settings. Type in the tags you don't want to see in the 'Blacklisted Tags' box. Use a new line to create multiple blacklists. If tags are placed on the same line, only posts that contain all of those tags will be hidden. For example,
nude male will hide all posts that are tagged with vomit, and all posts that are tagged with both nude and male. Post that contain nude but not male will still appear, and vice versa.
In addition to blacklisting based on normal tags, you can also blacklist posts by pool ID number (e.g. pool:1234), rating (e.g. rating:e), uploader (e.g. user:bob), or status (e.g. status:flagged).
You can also whitelist tags within a blacklist. For example,
spoilers -touhou will blacklist all posts with the spoilers tag, except for those that also have the touhou tag.
When your blacklist is active, a category called "Blacklist" will appear on the top of sidebar on the left. You may click on a blacklist entry there to temporarily disable it and show the posts that match.
The following blacklist is automatically set for anonymous users and new users accounts:
spoilers guro scat
Note that this only applies to user accounts created August 6th, 2015 or later. Accounts created before that had no default blacklist.