First thing to consider is your end purpose, what is the intention of your herbal oil? Is it scent, therapeutics, flavor, magic, color? If you are not quite sure of an intention and just want to experiment, than let yourself be guided by the plant that presents itself to you, it may be in a dream, from your morning pages or perhaps witnessing a plant waving to you.
For making infusions you can use either fresh or dried material. If fresh make sure your material is completely free of moisture by placing the plant matter on or between paper towels, tying up bundles and hanging them upside down from a rafter or by laying them out on a screen. Depending on the climate where you live, allow the plant matter to wilt for approximately 5-8 hours or more,
If using plant matter that is already dried double your quantity.
PLANT INFUSED OIL
There are just two basic ingredients to creating an infusion: plants + carrier oil. It is important to consider your end result when selecting the carrier oil. For example if its for flavor than an organic extra virgin, cold pressed olive oil well be perfect. For a perfume, that option may not be the best because of the scent, thus I would suggest jojoba oil, which is actually a wax and does not go rancid.
A 'preservative' for your infusion such as benzoin or Vitamin E Oil
Glass jar with airtight lid or canning jar
White wine or a high proof alcohol
Step 1: If using leaves make sure to remove wood and hard stems, unless you want those as part of the infusion. With flowers use the 'petals', not the inner regions such as calyx. In the photo below, after drying my sage I removed the leaves from the stems.
Here is a basic formula if you want guidelines:
15 gm dried herbs or 30 gm fresh herb
1 cup oil
Step 2: Place your plant matter in a glass jar, then pour oil over them, taking care that all of your plant material is covered. Cap with a tightly fitting lid. To help breakdown your plant material add 1 tablespoon of white wine or a high proof alcohol.
Step 3: Leave the jar in the sun, some individuals move the jar in the evening to warm spot. I like to leave mine in the window to observe the night energies which include stars and moon. The length of the process varies with each material, check in on it after for 2 weeks to see if it is to your liking.
Step 4: Remove the top and strain the oil. If you feel you would like it stronger then repeat the process using your infusion as the oil.
If you used a canning jar, remove the top, pop out the inner metal circle, layer the top of the jar with muslin, attach the outer screw rim of your the lid and strain your oil.
There are many other tricks of the trade and ways of working, for example you could plan your infusions according to astrology, if using flowers replacing them every few days is the best way to get a strong scent. The main thing is to do it and learn each time.