Do not spend an equal amount of time on each move. If you have to chose between two five-forced-moves lines, it's brighter to think five times as long on the first move and playing the other instantly.
Most chess players (including me) get a 'feel' for time control by practice only, but there is indeed a rule that you can apply without hesitation :
When a move is forced (i.e. you can see all other moves lose), play it before calculating it - you can think during your opponent's time, and if he answers immediately, he might have missed a better move, and it will be easier to calculate from that point anyway ; even if the move you played loses, it means you are lost anyway. (Even if, indeed, you need some minimal calculating before deducing a move is forced...) Example : your opponent has taken one of your pieces and you have to retake it, just retake, don't think of what you will do next.
As for a rule for time management, it depends a lot of the time control you play. Bullet under 3 min/player is mostly fast moving of the pieces and not chess ; from 5 to 10 min/ player you need to be able to calculate fast up to five moves ahead and 'smell' the evaluation of the resulting position. In longer time controls, you sometimes need to calculate 10-20 moves ahead in the endgame, spending much time on a line, to play it instantly after that.
EDIT : knowing the openings and their ideas saves you some time, but knowing some endgames also. If you know that king and rook can mate a lone king, you know that is you achieve a position with such a material on the board it is won, and you evaluate it as 'won' without calculating 10-20 moves to checkmate.
I'd like to hear how you all plan for something I'm not used to...... time. I've played many chess games, but never that seriously, or with a clock. I lost my first game with a winning position because I only had a few seconds left, and was just trying to make legal moves. Materially I was down, but I felt good about my position. After the game, I saw the glaringly obvious mate I missed on two different moves. Anyway, I wouldn't have missed if I had a little time to think. So...... Do you guys just assume 50 moves, divide that into the total time, or what do you allow? Thanks!