I'm not a great grappler or superior conditioned but I'm improving all the time. So, take what I do for what it's worth.
I like to do weights for conditioning. Like this morning I used a strongman log,farmers walks, sledgehammer and sit-ups for my morning conditioning. Since tonight I train BJJ, I did 3 sets of...
100log clean and press for 10 reps
80 farmers each hand for 100 feet
8 pound sledge for 20 hits on a tire
10 reps of laying on my back kicking up in the air.
3 sets non-stop...it took 8 minutes.I try to be explosive on everything I do. Next Monday I will pick 4 movements and shoot for 9 minutes of work.
Make a very small improvement every week(weight,timeor sets), it will prevent overtraining.