Learn from my mistakes and save yourself the time I've spent learning the hard way.
I've got naturally pretty mobility, verging on being hyper-mobile which you'd think is a good thing when you need to full squat with a bar overhead. It really is a good thing and I'm grateful for it, but not for the fact it made me lazy and often neglected doing proper stretching and mobility work. Long term this lead to a few niggles and minor injuries that when I do take care of the soft tissue work (rolling, massage, stretching etc) just don't seem to bother me at all.
There aren't many good athletes or lifters that can get away with doing no stretching of any kind. Don't be as arrogant as I was for a while and be sure to put in the boring work as well as all the fun stuff. Having no coach can mean that no one is nagging you to get this stuff done, in which case maybe check out the growing phenomenon ROMWOD or get yourself booked into a stretching/yoga class and outsource the motivation.
Rushing my warm ups;
This one relates to some other points I'll raise here too but specifically the problem of having very little time for training so not taking enough time to warm up properly. Weightlifting requires huge joint ranges, very fast movements and high loading so preparation is not only key for success but also to prevent injury. I keep a training log (see next point!) and can see when I had my best and worst sessions, usually the best being when I've had ample time and don't feel rushed. Not to say that I rest forever between all sets or that every session takes 2 hours (some do). Just that when I have around 15-20mins from the moment I begin training to my first real lift, I feel better, move more smoothly, feel less discomfort from end ranges, and often hit my best lifts.
My advice is protect your training time and prioritise your training goals so that your warm up is never compromised. That way if you do end up cutting things short they are the things that matter least or can be done separately another day.
Keeping a training log;
I haven't always done this, much to the detriment of my gains. Embarrassingly I was told to start keeping one in 2008 by a very well qualified mentor. I ignored the advice for about 3 years thinking that I knew better and that my memory was good enough. What a knob I was.
Since keeping a very detailed log (I use a Numbers spreadsheet to record all weightlifting sessions, noting every rep and weight and how hard each was) I can now see what works and what makes me feel like I've been run over. How often I need a low volume week and when I can really push the heavy singles. I didn't get immediately stronger or fitter or look any better naked - damn! - but long term progress has been far better than before and I'm the strongest I've ever been and miss fewer lifts than ever before. See my next point...
Chasing my fails;
Maybe it is just the arrogance of youth or maybe I'm particularly stupid. I would repeatedly attempt weights that I knew weren't going to come off, telling myself if I just tried harder that it was definitely going to happen. Some days it was due to fatigue and any other day with more sleep and less work I'd make that lift easily. Other times it was the programme - I just wasn't supposed to be at my best/peak at that time. The worst of it however was making a technical error that I could tell was happening, and repeating it over and over again because I didn't have the mind set or the right cue in my head to fix it.
Changing my approach from aiming for heavy singles each weekend (easy to do when you're a beginner because they aren't really that heavy yet) to following longer term programmes was really key. As well as understanding that a heavy single might only be 90% of my best lifts but for that day it was 100% of what I was capable of. Not getting disheartened by this and instead seeing it as "on a day when my legs barely function and I've slept only 5 hours I can still hit 90% of my best lifts, that must mean I'm better/stronger/quicker..."
Another rule I use now is the competition strategy. In a normal weightlifting competition you get 3 attempts at a snatch and 3 attempts at a clean and jerk. Therefore missing 3 lifts in training means you just effectively 'bombed out' (if you don't register a lift you can't have a total and are out of the competition!). Thinking this way lead me to make more sensible jumps in weight when going heavy, and to warm up properly too. It also helps to focus your mind and stop you endlessly attempting lifts that you shouldn't.
Knowing something is wrong but doing it anyway;
I went to New Zealand in Jan 2016 and did a couple of training sessions with arguably their best ever lifter Richie Patterson. I'd seen Richie win gold at the common wealth games in Glasgow and watched most of his lifts on instagram and youtube. One of the many nuggets of advice I got from Richie was not to even touch a bar until you feel ready. If somethings feeling off when you move around with a broom stick, fix it as best you can first rather than spend all session with it distracting you.
Going beyond this, don't load the bar until your technique feels right in your warm up sets. That might mean doing 5/6 sets of 3/4 reps with just the bar before your first set of loaded snatches. Practice only works if you're practicing that skill properly. Similar to the previous mistake where I would take multiple attempts and effectively practice failing, some days I would be making silly errors with an empty bar because I wasn't focused or being lazy or hurried. You can't do that and still make good progress in weightlifting. Each rep must be right, or at least right enough, to learn and get better. Having a coach tell you what's wrong is invaluable but you also need to feel it.
Think about this when you're going for those heavy singles too. Is the technical error(s) you're making going to disappear or explode if you add MORE weight to the bar?
Don't waste your time, I've made these mistakes so you don't have to!