For me, some of the best tips are keyboard shortcut or modifier keys and are not really hidden but I’ll post them anyways:
-Hold shift + Ctrl, left click and drag up or down on midi event(s) to change their velocities
-Hold Ctrl while resising an event (when snap to grid is enabled) to bypass the snap to grid and resise freely (same thing for moving an event)
-This is simple but a lot of people don’t know about this, use Grid Relative in the snap to grid panel if you want to move events but keep their starting position.
-when using the Range selection tool, hold Ctrl + Shift to select all tracks
-there’s a command called select cursor to end, so if you assign this to a keyboard shortcut and also assign one to split at cursor, you can easily split all files and the select all on the right side of the split to move them
-if you want to delete a section but you want all event after to move where the deleted section is while keeping everything on the grid use the range selection tool while snap to grid is enabled, use the ctrl + shift modifier I talked about to select the part you want to delete (let’s say you delete 2 bars), then go to the snap type in the snap to grid panel and change it to shuffle, then press delete. the 2 bars are gone and all event after moved to the left automatically. Don’t forget to change the snap type again after tho 
-Variaudio shortcuts: press tab to switch between segment and pitch modes, hold ctrl while moving a note to put it perfectly on the pitch, hold shift while moving a note to move it freely
-In mixconsole, alt double click on sends to make the send plugin show up
-Add a Key command to Find track/Channel (in my case it’s F) so when I press F I can start typing the name of a track and it will select it … this is really usefull to find tracks easily in big sessions
I could go on like this but I don’t want to clutter the forum I hope this will help some of you