One way is to infuse olive oil with lavender! You basically just pour some olive oil in a jar that can be sealed, sprinkle in a bunch of the lavender and mix it up a bit, seal it tightly, then leave it for 2-3 days in a warm, sunny place. When ready, strain it through muslin or cheesecloth. If you want to make it stronger, just repeat the steps: Put the oil back in the jar, add more lavender, let it sit, strain it again. You can also mix in some lemon (smells so wonderful!), witch hazel (for applying topically), orange, etc. You should store it in a dark brown bottle in a cool and dry dark cabinet.
You can put it in your bath, use it as a skin moisturizer and topical sleep aid, dry hair treatment, etc.... it's seriously fantastic!!
To extract the pure oil is much harder and requires a lot more lavender, so I usually just buy the pure stuff from my nearby organic shop and make the infused olive oil myself!