Personally, I find my biggest weakness to be time control/management. I usually end up moving very fast with a lot of time left on the board or move to slow with a little time left on the board. I am a little impatient so this probably has some connection with the speed in which I move, but I was curious as to how someone can improve their time control/management?
I'd nominate all of NM Dan Heisman's famous Novice Nook articles on Time Management (go to the link and search by subject). The *Two Move triggers* article is pretty insightful and most applicable to your posted question.
In addition, the best way to learn how to manage time is to make "time taken" a part of your post-mortem review. In other words, don't just write down your moves, also write down how much clock you've burned per move and when reviewing the game later, figure out if the time taken was indeed sufficient or not as you're probably going to start noticing things about that position that you didn't before. If you play online, turn on move-timestamps to track the time used for you.
When you get a game reviewed/critiqued by a stronger player, it is always worth asking "How much time would you take (for a slow game) in a position like this?". You'll find very interesting answers and notice telling deltas between your sense of time management and theirs! (they would really use their time in critical positions way more than you did but but spend very little on things that you probably worried a lot about).
One more problem that is kryptonite for my own time management is my current state of mind : lethargy, hungry, tired, over-caffeinated, distracted with other windows on my screen etc. ... I've signed up for G/120 games when I really only had it in me for a G/5 and vice-versa ... a lot of people tend to be confused about playing a time-control that's readily available (Hey, I can start a game right away!) vs. playing a time-control that's right for them but they need more patience (wait longer online) or have to put in some work (travel to a local club) in order to play it!!! A unbalanced diet of too much blitz (or too little of it) can often impair your brain's ability to gear-shift suddenly to games with different time controls.
I agree with the above answer, but from my personal experience, I handle time management pretty well because I am very conscientious about the time I spend on anything I do. If you are a person who is regularly late, I think writing the time taken on your score sheet will make you more conscientious of the time. Look at your time control for the game. Is it G90 or G30? That is 90 or 30 minutes for the entire game. Consider what is your average number of moves per game. 40 moves is reasonable to start. Do the math to see how many moves you need to make on average in 10 minutes. The point of all this is to just be more conscientious of the time you spend. For me, I factor in 1 long think of 20-30 minutes in a 40/2 G60 time control, and average the rest. See different time controls.
Practice by playing at a fixed time per move. Ten seconds is good, you could use 20 if ten is too fast.
Time up means you must move but also you must wait for time to be up to make your move.
this will train you to think some and avoid problems with fast moves that are bad. It also helps you move quickly in time trouble which wont happen often if you train this way. Usually you will be thinking on their time then moving soon so they are the ones who will have time trouble unless they also train like you did.