Where do most players block best? On the backhand. Where do most players attack the most? To the opponent's backhand. This never made sense to me.
When attacking there are three places you should normally go for: the wide forehand, the middle (the opponent’s crossover point between forehand and backhand, usually around the elbow), and the wide backhand. Most beginning and intermediate players probably attack to the backhand twice as often as to the forehand, and almost never to the middle. We’ll call it the 0-1-2 rule, i.e. they proportionately go zero times to the middle, once to the forehand, and twice to the backhand.
Instead, try the 3-2-1 rule, where you proportionately go three times to the middle, twice to the forehand, and once to the backhand. (This assumes your opponent isn't able to counter-attack with his forehand consistently, as they often do at the higher levels. If they do, change your attack placement accordingly, though it also might mean your opening attack is too soft, too short, or predictable.) Few players block on the forehand as well as on the backhand, and everyone's vulnerable at the middle. So why not go where the opponent is vulnerable?
There are exceptions to this rule. If you are going for a particularly difficult attacking shot from a wide corner, go crosscourt, where you have more table. (The table is 9 feet long, but about 10.3 feet crosscourt, about 15.5 inches longer, almost seven more inches on the far side.) Also, you have to take into consideration your own positioning. For example, if you are attacking with your forehand from the wide backhand corner, if you attack down the line you are vulnerable to a crosscourt block to your forehand (unless you are fast on your feet), so you might go to the middle or backhand. And, of course, if the opponent is able to consistently counter-attack with his forehand you might want to attack there less often.