Velocity is key
Even though you are undoubtedly aware of how crucial velocity is in and of itself, when programming a sequence by hand or mouse, it's frequently disregarded. This is likely because it can impede workflow and is a little laborious.
Since it must be done, a simpler method is to go back into each individual clip that you manually programmed prior to beginning the record's mixing process, and slightly adjust the velocities of the majority of the contributing parts.
Even though it doesn't seem like a necessary or significant task right now, your listeners' and your own subconsciouses will undoubtedly thank you in the future.
Velocity is crucial to making programmed midi-parts sound realistic, so don't skimp on this step—no matter how difficult it may be.
Just consider the notes that will be played and, more importantly, how the pianist might play them when sitting at a piano.
For instance, notes are frequently played in concession and are meant to "accent" or offset one another.
Given this, you should consider making some notes extremely quiet and others much louder.
Alternatively, you could just use the basic "low, medium, high" for every three notes. Just do what feels right for you and the song.
The drums are, to be honest, the instrument I hear the least of.
This is very unfortunate because, as anyone who understands the inner workings of a drum would attest, velocity is crucial.
A hi-hat can be quickly and effortlessly turned into a shaker (or tambourine) by just repeating the steps a few times, back-to-back, at different speeds.
Velocity has a tremendous amount of, well, power. Thus, once more, don’t ignore it.