Here are some clues for reading the board. No matter what cards are on the table, an opponent may have one pair, two pair or three of a kind. The three of a kind can be especially sneaky. There is no way to tell from only the cards on the board if your opponent has one of these hands. A straight requires there be three cards on the board, within a span of five ranks. Tedious as it is, you can simply count off on your fingers until you begin to recognize card groupings. Low and middle straights often come unnoticed. But, even a low straight beats a set so be on the lookout anyway. A flush requires three of the same suit on the board. Both a full house and a four of a kind require at least a pair of cards on the board. A straight flush has the combined requirements of a straight and a flush. Which only makes sense.
A quick procedure for reading the board: Look for pairs on the board. If there are none, you are safe from full houses and four of kinds. Scan for a possible flush. If there are not three of a suit on the board, you are safe from a flush. If there are three of a suit on the board, scan for a possible straight using the suited cards only. If you can make a straight from them, there is a possible straight flush on the board. Scan for a possible straight using cards of all suits.
When the Board Pairs: When the board pairs, strange things can happen. Someone may be holding that exact pair in their hand, completing a four of a kind. More likely, someone can use that pair to complete a full house. A player can have a “split” full house, where they have one card the same rank as the pair on the board, and another card that matches a single card on the board. For example, I hold AQ, and the flop comes AQQ. I have made a full house, Queens full of Aces. Another way to complete the full house is the sneaky underdog full house where a player matches a single card on the board with their pocket pair. For example, I hold TT and the flop comes QQT. I have a full house, Tens full of Queens, but am likely to get a lot of action from anyone holding that remaining Queen in their hand. This hand is a favorite of mine, and I look for it as I’ve won (and lost) a lot of money on it. Another phenomenon that takes place when the board pairs is that your two pair loses to an overpaid. For example, I hold TJ, and the board shows TJ26. My opponent holds Aces in the hole. When the river card comes, a 6, his overpaid, combined with the pair on the board beat me (my two pair TTJJ6 vs his two pair AA66J). This is just another reason why when the board pairs, people take notice.