I'm not the strongest guy in the world, so I started out in the bottom. Felt more comfortable in close guard then on top. My gym has a lot more heavier guys than smaller guys and even our smaller guys destroyed me when I started.
I developed closed guard and half guard first, then open guard (spider guard/de la riva). I drilled deep half guard for about 6 months before it became something that I actually LIKED to do instinctively rather than tentatively. From these guards I've become better at sweeping allowing me to work on my top game more, knee on belly, side control and mount.
Next up I'd really like to get better at taking the back, back attacks, and even dabble in butterfly.