Focus on control positions that lead to easy subs that can be finished either top or bottom more so than focus on sweeping, passing, and traditional positions.
You can go really far just learning the big 4. Note that these 4 usually can chain back and forth into each other. They're also all great because for the most part you don't need to pass the guard or even get a clean sweep to get to any of these. The back is the closest to a traditional position but you can still even get it any time their back is off the floor.
1. back control: rear naked choke, armbar, triangle, back triangle
2. leg control: outside and inside heel hooks from outside ashi, 4-11, etc but the 4-11 is king.
3. front headlock: guillotine, darce, anaconda, japanese necktie
4. kimura control: kimura, armbar, regular/reverse/inverted triangles
Besides that I would focus on endurance, staying relaxed to conserve energy, and spiderweb and back position offense and escapes if there are EBI style overtimes.
Also conserve your energy. Sub only is a marathon.