First step is to locate an unpolluted area with dandelions. Make sure there are no roads nearby and that the area (or nearby areas) hasn't been sprayed.
Wash your foraged dandelion greens, flowers and fresh dandelion root thoroughly to remove any dirt or bugs
Chop everything up.
Place in a jar and cover with alcohol (preferably organic alcohol, or grain alcohol such as potato vodka).
Leave in a dark, cool place for about 4 weeks, shaking the jar occasionally
After 4 weeks, if the tincture has reached your desired potency, strain the leaves, petals & root with a fine mesh strainer.
Store in an amber tincture bottle with a dropper top.