There are more ways than one to encounter a dragon. With a low level group it's obviously not feasible to meet one in its lair and fight it. But standing on a bleak moorland, utterly exposed and vulnerable, it can be a chilling experience to see something flying far far overhead. Something that could just be an eagle, but you never know...
The PCs are setting up camp at the end of their first day of walking through the Esh-Inel Mountains, when they hear in the distance a low rumbling, like thunder. It grows progressively louder until it echoes off the mountainous bowls around them, then dies away again. At its worst the ground starts trembling. It happens every day at this time, and it is the noise of the Great Carts on the dwarfish underways returning home after a day mining, laden with many tons of ore.
A character who is undergoing changes of personality (like buying off mental disadvantages - flaws - or changing alignment) might confront personifications of aspects of his personality in dreams: a griffon representing the courage he needs to face a terrible foe, or a satyr standing for the lecherousness a warrior must overcome to be admitted to an order of knights who must uphold vows of chastity.