I would suggest practicing more with grids. Using a grid you can have (for example) 4 across on desktop, adjust that grid to 2x2 on tablet, and adjust it to 4 down on mobile. Or whatever variations you want, but if it is setup properly from the beginning it makes it easy to adjust for each breakpoint. You also will want to pay attention to how the elements inside the grid are positioned, docked, and sized as that will all make a big difference as well.