I'm assuming most people working on this kind of art are already familiar with actions, but for new PS users I thought it might help to introduce them to it. You basically just record a few actions, then you can perform all those actions with a single click. Great for repetitive tasks. Just create two new actions, one for 780 and one for 290.
New action > 780 (or whatever name you want) > record
Image size = 780 px (constrain proportions) (or 290 depending on the size of the art you're working on, or which action you're trying to record)
Canvas size = 800x310 px
View > clear guides
View > new guide > 10px vertical
View > new guide > 790px vertical
View > new guide > 10px horizontal
view > new guide > 300px horizontal
After that you just edit your art, and when you're all done just select the action and hit play and it will automatically center the art, with the 10 px gutter, with guides to check your work. Just be sure to hide your layer effects (drop shadows, etc) before running the script. Then turn them back on when you're ready to save the file.
If you run the script and parts of your art get off, just ctrl + alt + z a few times to get back to where you were (or use the History menu to go back before "trim"), then run the other script. *Added "guides" to the script.
Last edited by burcs
on Sat Jun 25, 2016 3:26 pm, edited 1 time in total.