Blob Tool - Instead of a regular brush stroke, painting with the blog brush gives you a filled, compound path. Any new shape painted with the same color and stroke will automatically merge with existing shapes with the same settings.
Brushes (learn how to create a brush then apply as a stroke on a circle) -ART BRUSHES - learn how they work and play with them -Scatter Brush -Calligraphy Brush -Pattern Brush
Brush Tool - Lets you stylize the appearance of paths. You can apply brush strokes to existing paths, or you can use the Paintbrush tool to draw a path and apply a brush stroke simultaneously.
Change color of guides - Edit > Preferences > Smart Guides
Smooth Tool - You can smooth the appearance of paths as well as simplify paths by removing excess anchor points
Live Trace - allows you to create vector art from a photo, sketch, etc.