In an ideal situation, you should have three types of randori partners:
i) Those who are lower level than you
ii) Those who are equal level to you
iii) Those who are higher level than you
It is important to have some players who are lower level than you because you need to be able to get in some throws. If all your training partners are better than you and you never ever get to do any techniques successfully, you will never acquire mastery of any techniques. In time you will lose heart and start to doubt your abilities in judo.
Rules of thumb when doing randori with those who are lower level than you:
i) Try new throws that you have not yet mastered. This is your chance to actually get a good feel of how these throws should feel when executed successfully.
ii) Try new combination attacks for the same reason above. This is your chance to actually get these combinations to work.
iii) Try techniques to the other side (if you are right-handed, try some left-handed techniques). Again for the same reason above.
iv) Don't waste time doing techniques that you have already mastered. If you are already very good at ippon-seoi-nage, why do this technique on a lower level player who will easily fall for it? All you get is a cheap thrill of throwing someone easily. But you learn nothing from it. So, don't do it.
In a nutshell, when you fight against a lower level player, use that opportunity to try new stuff.
It's good to fight someone of equal level because they can give you the right amount of resistance to make it hard for you to throw; they can potentially counter you when you come in with a sloppy attack; and of course, they could potentially throw you, which gives you a chance to develop defence and countering skills.
The potential downside of fighting someone your equal is that the randori can easily slide into a shiai and both players' mindset becomes one of a contest rather than free-flow sparring. This is not good. It becomes a clash of egos with neither one willing to give an inch, fighting defensively and refusing to take any risk. That doesn't benefit you because you don't end up doing anything other than preventing your partner from scoring.
The other danger is that the both of you might get injured. When pride is at stake, players will be tempted to spin out of throws to avoid conceding any score, almost at all cost, just as they would in a competition. Each time you do that you are risking injury. There is a time for doing shiai style fighting. Randori isn't that time. Randori is a time for you to attack without inhibitions. Get countered, no problem. It's just randori.
If you have a tokui-waza (favourite technique) that works well for you, use it against an equal level partner. They might be able to defend against it or even counter it, which will force you to improve your tokui-waza.
For years, I had made the very mistake I wrote about above. I had a training partner who was a bit younger than I was but like me, was a former national champion and international competitor. Our randoris were always like shiais where neither one wanted to concede any scores. Looking back, I now realize that I had made a classic mistake that cost me a lot. I didn't improve my skills because I was too concerned about "winning the randori" and I got injured a few times trying to spin out of throws.
Don't make the mistake I did. Randori is not shiai. It is not a contest. Leave your ego at the door and don't worry if your technique fails or if you get countered. Nobody is watching (they are all too busy doing their own randori). So fight hard and enjoy the randori.
No matter how good you get at judo, there is always someone better. And if you're lucky, that someone better is in your club. Always seek out those who are better than you for randori.
One of the biggest mistakes players make is to always seek out inferior players (this happens quite often). Yes, there is value in sparring with inferior players, as explained earlier, but if all you do is spar against inferior players and slamming them with your favourite technique, your judo will not improve. It's also not enough to fight with equal level players, you must seek out higher level players as well.
A higher level player will normally be able to withstand your attacks, so go after them with heart and soul. Attack, attack, attack. Don't hesitate and don't fear either their attacks or their counters. Know that the better player will inevitably throw and counter you (that's why they are called "the better player"). So, don't concern yourself about that at all. It's going to happen. Instead of anticipating (and fearing) their attacks, you make sure you put in your attacks first. Attack relentlessly and fearlessly. Although many attempts will fail, occasionally something might just work and you will learn a whole lot from that.
Come for Randori at KL Judo on Sundays
In Malaysia, it's always a challenge finding enough randori partners (the sports schools are an exception). At the recent SEA Games in KL, I had a conversation with a male judo player in his early 20's who told me despite the fact that his judo club has many members, he has only two players whom he can do proper randori with (and one of them wasn't even in his weight class).
This is because in Malaysia most judo clubs have very few adult players. Most are children. So children will have plenty of opportunity to do randori but not so when it comes to older teens and adults.
At KL Judo Club many of our members are adults with a wide distribution of weights. Our smallest player is 52kg and our largest is over 100kg. Besides our regular members, we also have many guests from other clubs and other states (and sometimes other countries too).
When you come to our club for open mat randori on Sunday nights, you'll definitely be able to find someone your size to do randori with. In fact, you'll probably find several your size. So, if you are in KL on a Sunday night, come join us for some free-flow sparring at KL Judo Club. We have the best randori in town.