Some useful hotkeys and actions

Selection

Ctrl+Up   Increase nodes size
Ctrl+Down   Decrease nodes size
Ctrl+Right   Increase edges weight
Ctrl+Left   Decrease edges weight
Cursor keys   Move by one pixel
Shift+Cursor keys   Move by grid step
Shift while moving   Move with vertical or horizontal snap
Ctrl while moving   Clone selection
Ctrl+Click   Extend/contract selection

Workspace

Ctrl+A   Select all objects
Alt+Cursor keys   Scroll visible area
Ctrl+ +   Zoom in
Ctrl+ -   Zoom out

Labels

Double click   Begin editing label
Enter   Start next line
Esc   Finish label editing

Polylines

Double click+Drag   Create a node
Right click on a node   Remove node