When you are playing no limit holdem you need to concentrate a lot in making sure that you are making your action within a short period of time.  At the most your response time should be the same whether you are playing straight or whether you are playing bluffs.  The response time should not reflect what you are holding.  Suppose you are trying to slow play and are taking a lot of time in making your bet then the opponent might probably get a clue about your response time as your are thinking, they will likely correlate your playing pattern, response time, and resultant bet to arrive at the situation you are probably working at present.

In no limit holdem you need to make sure that you are keeping your opponents guess the wrong thing about you most of the time.  When you want to make them think that you are better, you need to play poker accordingly.  This can be accomplished by modifying your tell.  You can occasionally burst out of your normal response time making them believe that you are slow playing or fast playing or whatever.  If you are going to keep the opponent completely confused about the kind of view they can have about you, then you might not be able to use it to your advantage.  Sometimes their confused decisions can be very bad for you.

When you play no limit holdem you need to make sure that you make the opponents behave the way you want them to be.  You will have to make them think what you what them to exactly think.  To do this you will have to exactly play straight in a way that they can easily pick up some tells and then you can later on modify things. Before you can actually bluff in no limit holdem you have to make others believe that you are a straight player.  This is very important if you should get results out of your bluffs that you make occasionally.

Whether you play no limit holdem or any other game, there is no real need that you should be bluffing to make the win, rather you can play straight and good, but to meet up with occasional challenges you might have to bluff if you should win.  So, make less bluffs brilliantly and use them to your advantage sparingly.