I think that the three things that made the biggest difference in my dehydrated skin was:
1) the way i washed my face. I used to wash with a foaming cleanser in the AM and PM. I started just washing with water in the AM and using a cream cleanser (La Roche Posay Toleraine Hydrating cleanser) in the PM. I don't wear makeup so this is more than enough to cleanse at night.
2) Using moisturizers with ceramides and squalene. In the AM I started using the Ordinary's natural moisturizing factors (ceramides) and in the PM I started using oilatum natural repair (squalene). This second one is actually discontinued now (so sad) so I'm in the process of testing replacements: Avene's cold cream and Ren's emollient rescue cream (this one is expensive but so good) are both excellent contenders at the moment, testing them out with great results now.
3) Hyaluronic acid. I started layer the Ordinary's HA serum over a mist of water and under my moisturizer AM and PM and it made a noticeable difference in my skin's plumpness and just general health.
I love TO's Hyaluronic acid + B5! It plays nice with my CeraVe and I like actually like the slightly tacky feel as it goes on. If I add a drop to my foundation it really seems to help it blend and prevents dry patchy areas on my cheeks or by my nose.