Hard difficulties are considered the second most difficult in the general of 4 difficulty mapset. This difficulty level between normal and hard difficulty is considered enormous and is considered by many one of the hardest learning curves.
These maps generally have a higher Approach Rate, HP Drain rate and Overall Difficulty compared with Normal difficulties. More complex/difficult patterns also appear in this difficulty such as short streams and jumps. Depending on the mapper's ability and the song used, this name will be used instead of Insane, based on mapper's relative comparison on testplay results.
If your map has a Hard difficulty you should try to keep the map considerably easier than the Insane (avoid big jumps and fast/long streams).
A commonly used technique to map Hards for faster songs is a simple pattern of 1/1 Sliders and 1/2 Circles between them (sometimes left out to create small pauses from the speed, especially when played with DoubleTime).
Try to not create a huge gap between your Hard and Insane difficulty, it might unbalance your entire mapset.
Following mostly "what you can hear". Try to capture the essence of the song and don't leave out too much. Interesting patterns and beat placements are encouraged along with jumps and short streams/triplets. If your mapset features a Normal and an Insane make sure your Hard map is a reasonable stepping stone between them.
Difficulty setup should include a BPM appropriate slider velocity that captures the pacing of the song. Use multiple slider velocities if needed. Drain rate and hit accuracy should balance the difficulty of your patterns and the frequency of streams and other 1/4 notes. Approach rate should be balanced between the BPM related note density and the readability of more complex patterns.
And try to avoid these:
An ideal setup for a Hard difficulty would be:
Typical difficulty settings for Hard.
These are just ideas of how the difficulty settings will be like - set it to how you find fit!