i have had serious problems with the clock in active tournaments (25 to 30 minutes time control, no increment) so I generally try to play faster lest i lose on time, yet this has affected my play and quite often the result of the games too.
one colleague has suggested that i divide the 25 minutes into:
5 mins for the opening
10-15 mins middlegame
and 10-15 mins ending
but is this the right way to do it?

Naturally it depends on the situation.

But generally I would say: spend more time on the middlegame. Endgames are important and all but at these timecontrols there isn't just enough time to do it good (unless they are fairly standard and we are all supposed to know these by heart int his perfect world we live in).

I might play the occasional online practice game at those speeds, but I'd never enter a tournament with a time control faster than an hour.

--Fromper

I threat 30 min as an extended blitz game where you can spend a few minutes thinking about the more complex positions. I do find it a relaxing kind of time control. Not as stressfull as blitz and not so intense as a long game.

That is my interpretation as well, 30 minutes is still pretty fast. It does give you time to slow down and think about what you're doing though, but your opponent can do the same. I've always found it curious that games with a time controls 15 minutes or more are so rare on internet servers, compared to the abundant 1, 2 and 3 minute (no increment) games, which seem to be all about not getting mated while moving faster than the opponent in order to flag him when his time expires..

Here are some general guidelines you may find helpful when it comes to time management.

Openings:
1- No matter how well prepared you are, in games below the master level you will generally find yourself quickly out of your opening book. It’s a good idea to be familiar with the recurring patterns and motifs in your selected openings. You achieve this by playing over a lot of games with your selected openings. That way when you are out of your book knowledge, you can quickly grasp the overall strategy you should be adopting.
2- Opponents will often play openings you are unfamiliar with. When that happens your best chance is to spend a few minutes assessing the position to try to gain an understanding of the general direction play is likely to take. Be careful not to use too much time because if you fall behind on the clock, you will likely be in time pressure later.
3- When you’ve reached the end of your book knowledge take a minute to determine if the game is going to be a tactical or positional battle. If it’s going to be a tactical battle where the result is likely to be determined by a tactical error you have to make sure you spend enough time looking for tactics so that you don’t miss any. If it’s likely to be a long positional battle try to make sure you don’t fall behind on the clock because you’ll likely need time later. In any case the nature of the looming course of the game, tactical or positional, will help determine how much time you need to devote to selecting your moves.

Middlegame:
1- Have a plan. Evaluation and planning can be done on your opponent’s time. When it’s your turn you can calculate variations.
2- Calculate accurately and swiftly. We often lack the courage of our convictions and too often check and recheck our calculations in fear we’ve missed something. This will take some practice in the art of calculation.
3- Once you decide on a move, play it! It’s a fact that after you’ve decided on a move further calculation is unlikely to cause you to change your mind. That said, prior to moving a quick blunder check is in order.
4- Don’t worry about what you should have done on your previous moves! It’s too late and doing so will only harm your play.

Endings:
1- A little elementary knowledge of things like opposition, triangulation, counting, etc. will save a lot of time because you will have an idea of the correct procedure which will make your calculations go faster.

I’m amazed how many people think a 5 minute game with a 5 second increment means the winner is going to be the one who amasses the most time on their clock. In one game I had 1-1/2 minutes left to my opponent’s 8+ minutes. I got cussed out in German for using an engine.

5 min + 5sec/move is a different ballgame then 1-2-3 min + 0 sec/move.