Can you talk me through what I should be doing for some dewy skin? Any suggestions on decreasing dark circles under eyes?

 I would suggest for you: Coolyptus Cold Cream, Glycolic Facial Tonic and the Face & Neck Toner.
These products are versatile. They don't have to all be used the same time/same day-as long as you develop a daily routine of cleansing and moisturizing.
You'll probably notice a difference even the first time using them. The Face & Neck Toner is not just a toner but a gentle wash and it's superb at reducing inflammation (I use it under my eyes especially). The other ones will naturally help your skin increase it's own collagen growth and help heal your skin as well. The Glycolic Facial Tonic has glycolic acid in which will lighten any scars and dark areas.
PS-dark circles under the eyes are many times an internal issue. It can be a  simple fix like making sure you get full REM sleep per night and drinking enough water. Sometimes it's a dietary thing and something needs to be changed so your liver and gut function better at removing toxins from your body.