Semi-Bluffing

Bluffing when you have absolutely nothing in your hand, not even a low pair, is pretty much suicide.

For starters, if you get called and they see you have NOTHING, ABSOLUTELY NOTHING, you've just cemented your reputation as a bluffer.

#2, if THEY are bluffing, or semi-bluffing, you just lost.

Lets take a flop, say, 3-5-10, mixed suits. Somebody places a small bet.

You call it with 5-5

Now, you have to know what SMALL means for them? You've played against them for 30 minutes, what do they throw out when they have the winning hand versus having SOMETHING.
If you don't have even this much knowledge of your opponent, you're not ready to begin bluffing.

You're putting THEM on a 3-3, a 5-5, or some kind of hopeless straight draw.

Nothing of interest happens on the turn or river. They don't increase their bet, nor fold.

Let's say the table now looks like 3-5-10-J-7

You toss out a big bet, a semi-bluff, hoping to convince them you have either 10-10, or J-J.

If they fold and you win, great. If they call and you win, great. If they call and you lost, well, you don't look like a hard-core bluffer, just someone who overplayed their hand.