For those who struggle to make classes etc Mine is do your fitness work whenever you can fit it in,unsocial hours or not,I run in the early hours and do weights on my lunch break 3 days a week. That way at least you'll get more out of the sessions you can attend,instead of just trying to catch your breath. Add yours.
^ good tip Mine is to accept personal responsiblity for my own study, on a practical level it means writing my overall own game plans, trying to stand/transition/sweep and submit from as many places as possible.
I work on my strength and conditioning when I can't make classes. Something you could do is work on visualisation of the techniques you know. Find a quiet space and imagine yourself doing a technique again and again.
As others said work on fitness and form. I work shifts on an engineering desk and I had to cover a lot of vacant shifts recently meaning I cant get to class as often as I want. Getting creative is important, I have a external stair case outside of my office so I use the underside for chin ups and use a wall for some exercises like hand stands and lightly firing off kicks and seeing how many I can continuously do in a set (although I did get some funny looks from security on my last night shift!) and I have some kettle bells I have in the office as well. I also bring in my training arming sword and shield so I can do timed rounds as well as shadow boxing. On a plus side I will be able to afford my armour soon
Now pull ups and maybe some very basic kicks are ok,but I wouldn't do anything too technical. You could be ingraining poor technique and not realise it,as tempting as it is.
Been training for many years so technique is pretty well ingrained. I do agree that if someone has limited training that it can lead to more issues that it solves. Working on fitness and strength training is normally more emphasized through.