Start with One Voice
The most common mistake new players make is trying to control all four blobs at once. Resist this urge. Start with a single blob -- the tenor is a good choice because it sits in the middle of the vocal range. Focus on creating a simple, singable melody. A good melody has shape: it moves up and down, has a high point (the climax), and returns to a resting place. Think of it as telling a story with pitch -- departure, adventure, return.
Use Stepwise Motion
Many singable melodies combine stepwise motion with occasional leaps, but there is no single formula shared by every memorable tune. In Blob Opera, try a slow connected contour, repeat it, and then change one leap. Comparing the versions is more useful than treating a stylistic suggestion as a universal rule.
Pay Attention to Phrasing
Just as spoken language has phrases separated by breaths, music has phrases separated by pauses or held notes. A good melody breathes. Try creating short musical phrases of 4 to 8 notes, separated by a held note or a brief silence. This gives your listener time to absorb each phrase. Listen to how a singer would perform your melody -- where would they naturally take a breath? That is where your phrase should end.
Vary Dynamics and Vowel Shapes
Drag speed and position affect more than just pitch. Moving a blob slowly creates smooth, connected notes. Moving it quickly produces more dramatic transitions. Holding a blob steady at the far left produces a bright 'ah' vowel; moving toward the right softens it to 'oo.' Use these dimensions to add emotional color. A climax might feature a high note on a bright vowel, while gentle passages work well with softer vowels.