One of the bigger problems with judo coaching is that movement and gripping are rarely taught explicitly. Simply asking questions helps. If you were getting dominated, ask the guy how you could escape or what bothers him from there. There are huge amount of little tricks and gripping techniques that experienced judokas pickup over time that are very helpful but are rarely asked,
Gripping is dynamic. You can't rely on just one grip much like you can't just rely on a single position in bjj. As in bjj where most people have a favourite position, most in judo have a favoured grip. Again much like bjj, it's important to have techniques for every gripping situation. I find that generally when i'm getting dominated by grips, it's because I lack the tools/techniques to work from there. You have to adjust your grips and movement patterns depending on who you're fighting and how the fight is going. If they're shorter than you, you might use a high collar/over the back grip to control them. If they're stronger/taller than you, you could might try to outwork them, make them move, don't let them get control of you. Quick drop seois, sodes, leg grabs and kata gurumas straight off the/before the initial grip can be very effective against taller/slower guys. Fighting someone in your own weightclass is when you can usually work your preffered grip game.
I use that high grip a lot myself. Works well for me because i'm usually a bit taller than guys in my weight class. I have various things i do from there. For instance if the guy trys to defend by going into a jigotai(crouched defensive posture) i'll usually grab the belt which i find easier than most due to my longish arms. The Russian Judo Masterclass book had a lot of good stuff on belt gripping
The Neil Adams book is good. Lots of ideas on what to do from various postions as well as some nice little tricks. It has some exercise to increase you're grip strength and gripping speed(which is often ignored), which are also quite useful.
Last thing i'd say is try and adapt about 6-8 throws and be able to use them in most situations. Being able to do 40 different throws on a white belt in randori might look good, chances are though, as a jack of all trades master of none, you wouldn't be able to use any of them on a decent black belt. Also try and have some variety with those throws, don't just rely on a single groups of throws(ie footsweeps).
