There are a few rules to good storytelling, and Lucas, with the PT broke many of them.
First rule: One must always SHOW, not TELL things about characters (it is different, however, for plot changes). Merely stating that two characters are friends or are in love is not enough. Show it, don't tell it... Obi Wan and Anakin, as we're told, are "friends". However, that isn't evident until ROTS, and even then it's still a bit lacking. We're told that Anakin and Padme are in love, but merely stating something does not make it true...
Second rule: Never dedicate too much attention on minor characters who add little-to-nothing to the plot. Lucas, especially in TPM, focused much on Jar-Jar. The character not only was annoying, but wasted time on screen... He added nothing to the plot, story, and so-on. Given, other storytellers, such as Tolkien, have broken this rule as well (such is the case with Tom Bombadil, who I believe to be the Jar-Jar of LOTR). Tolkien was a master storyteller, but the character of Bombadil has been criticized much since his appearance. (Thank God Jackson cut him from the film.)
Third rule: Never let the gems (i.e. landscape, music, etc) steal from the story (or in this case, steal from the film). These components are meant to be positive endowments to the story, not overshadow it. The PT is not remembered for story, but for its components (e.g. the action, cgi, etc).
There are many other rules, but these three reigns supreme when I think about the PT...