Serving is considered the "trick" part of table tennis, and this is where you can be most artistic. While you don't want to rely too much on trick serves to win, having a few tricky ones really helps - both in scoring a few "free" points and making your other serves more effective since they have to guard against those "trick" ones. (If overused, receivers get used to these "trick" serves and often find them easier to attack then simpler serves, such as short, low ones that set up a third-ball attack.) "Tricky" serves are often long and spinny, but may also be fast and dead, which opponents often put in the net.
If you don't have a few tricky serves to throw at an opponent, and the opponent does, guess who is at a disadvantage?
However, most serves should be "third-ball" serves that are difficult for opponents to attack and set up your own game, usually some sort of attack. (Most should be short, and yet long enough so that the second bounce would be just inside the end-line. At lower levels, you can serve long much more.) But even third-ball serves can and should be tricky. Try varying the swing and especially the follow-through right after contact. If you are serving backspin, follow through with an exaggerated upward swing; if you are serving topspin or sidespin, follow through with an exaggerated downward swing. Use quick motions to make it tricky for the receiver to pick up the racket direction at contact. If you serve no-spin, use a big, exaggerated motion and maybe even grunt on contact.
Don't serve just to put the ball in play; the serve should put pressure on the opponent, set up your shots, and win you some free points!