You could look at dermtv.com. That's the website of a dermatologist, he also makes videos on youtube, very instructive.
I do have rosacea, and it's a pain to deal with. Regardless of the origin, when your skin is on fire, treat it like a burn. I like to spray some thermal water on my cheek (like La Roche Posay or Avene), then when it has cooled down, i apply my spot treatment for rosacea (Avene as well, they have a specific line for rosacea). A hydrating or soothing mask works well too, or simply a cream for burns.
For the skincare itself, i think the only valuable advice is to take care of your skin and be gentle with it, no matter if it is allergies or rosacea that cause the redness. I use a milky texture to wash my face and remove my makeup, it's the most gentle thing i have found. Then i follow with serum, and moisturizer with spf. I use a night cream, and i rotate between textures, in winter i use heavier creams, in spring and summer i will go for lighter textures (i have combination skin).
If your redness comes from allergies, skincare brands have developped specific lines for what they call sensitive intolerant skins. This combined with your antihistaminics works well (i also have allergies so i know it helps). The only downfall is they last 12 hours, so technically if you want to be covered, it's one dose in the morning, then one before going to sleep. In that case, know what things you are allergic to. If it's pollens, it's vital to know when they rise in spring or summer, and start your treatment before.
If you have rosacea, at least get a specific treatment for your red areas (for me it's cheeks and nose), if not the whole line. All you can do in that case is slow down the process, wear sunscreen, avoid certain foods like spiced meals or red wine that are known to cause redness. But the only real treatment is laser.