Hand Range

I recently ended a few month break from poker. I am a fairly consistent winner at 6max .25 .5 limit holdem. Before i took a break I was getting fairly good at puttin people on a hand. The odd thing is that i was doing this without putting people on a range of hands. Now that i have started playing again I believe that this is my one biggest weakness. I think that if I am able to start doing this then I will get to know people a lot better at the table. I guess my question is how important is it to actually put people on a range of hands. I cant imagine its not important, I just want to know what you have to say about this.

Putting people on a range of hands is extremely important pre-flop (unless you hold the monsters AA or KK).

If you hold a good but not great hand - like AQo or a pair of 9s - it's essential to know if the villain raises the top 5% of hands or the top 20%, in order to calculate both your showdown equity and implied odds.
It is also imperative to consider the stealing range when you are in the blinds facing a steal attempt. Some players try to steal with only 15-20% of the hands, others do it as much as 40-50% of the time; you need to adjust your actions accordingly.
You can look up some examples at the Pre-Flop Raise section of this Poker HUD guide.