Cut your lavender from the garden. If you don't grow any you can buy it from the store. I have bought some (for baking needs) at a loose leaf tea store.
Tie bunches of lavender with elastics. Do about 5 stems per bunch, not too many as you don't want mould to form. Use an elastic to tie the bunches because as the lavender dries the bunches may shrink.
I hung mine from a railing so I made loops on a string and put paper clips through the loops. I then put the paper clip through the elastics wrapped around the lavender and hung them upside down.
Don't hang the bunches too close together, we want them to dry and not get mouldy. Hang in a dry place for a few weeks until dry. I hung mine for a few months and they were still very aromatic.
Crumble the flowers off. Some people use a rolling pin but I did mine by hand to ensure I got all of the flowers.
Use the stems for something like a fire starter in the fireplace or break the stems up and use them for the sachets as well. I broke them manually (time-consuming) but you could try a grinder.
Get your tulle or something comparable for the sachets. I found this at Walmart but I probably used less than half of it.
Cut a small rectangle of tulle. The size will depend on the amount of lavender you use. Experiment until you find a size that works.
Cut a piece of ribbon to tie around the sachet. Once you find a length you like, pre-cut a bunch to have them ready.
Put a bunch of lavender on the tulle.
It's ideal to place the the lavender in the middle and gather the ends up but I found some pieces would fall through the tulle. Place a bunch of lavender near one end and roll it up a couple times.
Gather the ends and pull up.
Tie a ribbon around the satchel.
They make great gifts! Place by your bedside, in your dresser and at work for a peaceful scent.
If the scent gets weak rub the sachet to release more of the scent. You can also add essential oils but I haven't tried that.