Trying to guess opponents' cards

I try to guess all the time because I use a HUD and it's easier. I have a lot of data/info, percentages, charts....

I try to guess every time even though the most time I got the wrong answer. Still need to practice more.

I'm not good at guessing the cards per say, but I try to read his general behavior - to see if he beats my hand or not.

Yes, it's fun to guess until you get guessed out.

I find that a min raise pre flop is completely unreadable until further action taken.

I think trying to estimate an opponent’s range is a given, and it gets continually refined the further a hand goes. But I think that taking it next level is to take a stab at what the opponent thinks you have based on your betting patterns will help even more (and this is based on the interaction between your betting patterns and your opponent). I think this is what people mean when they ask you what you are representing with your action. Once you figure that out, your bluffs will be so much more believable because it needs to fit the range you are representing.