parts one and part two of a post on Lush's claims).
The main ways to use botanicals are through powdered extracts, liquid extracts, and hydrosols. (Please don't make your own infusions or teas for your product unless you're a really experienced formulator with botanicals.)
Liquid extracts and hydrosols are easy to use. Just pop them into the right phase - compensating by removing some of the water - and you're done.
With powdered extracts, I suggest dissolving them in a little warm water (below 50˚C) before adding to the cool down phase. It'll mix in far better than just dumping the powder into your product, and you can remove that titch of water from the heated water phase if you're worried about having too much liquid.
Most solubility rates are determined at 25˚C, so we know it will dissolve well. We also know that the powdered extracts should be added in the cool down phase at 45˚C to 50˚C, so this is a fine temperature that won't ruin the extract.
Some extracts can mess with your products, so make sure you aren't making a big batch of lotion the first time you use something like green tea extract (it can cause redox reactions in a product, but that's for another day...) Try a titch in a 100 gram or 200 gram batch to see if you like it. And remember not to combine exfoliating extracts together (so papaya, apple, and AHAs together would be right out!)
If you're duplicating a product and don't have the extract, try it without. It might be that your hair or skin likes the product just fine without it or it could be at such low levels in the commercial product that you don't miss it! Extracts are nice little bonuses in our products, but we can still make something awesome without them.
Botanical ingredients of any sort - our extracts and hydrosols, but also things like hydrolyzed proteins, clay, and aloe vera - can be hard to preserve, so I suggest using your favourite broad spectrum preservative at the maximum amount (I like liquid Germall Plus at 0.5% but occasionally I use Germaben II at 1%).
If you want to make your own honey, glycerin, oat protein, or any other type of water, just add the ingredient to the water as you weigh it, and you're done! Pretty simple, eh?