The good news is that while psoriasis currently has no known cure and is a life-long disease, the available treatments are generally quite effective.
As with anything, the success of your treatment depends a lot on your doctor. The best way for a psoriasis patient to get treatment is to find a good dermatologist. Don't settle for a doctor until you've found one that seems super qualified. Even then, make sure you ask lots of questions and explore every avenue; doctors just aren't very good at giving you the full picture. For example, it took years before I knew about nail pitting, psoriatic arthritis, etc.; I had to do my own research, since the doctors didn't inform me. Doctors will also often prescribe crappy meds that frustrate the patient, like greasy ointments and foam (the "new" Enstilar spray foam is awful), or creams for the scalp (which is nonsense, use a liquid solution or a spray!). A disease this complex really should come with a manual.
As I keep telling people, the most important part of psoriasis is getting it under control. It's not a life-threatening disease, it's just an icky one that impacts your sense of normalcy and well-being. (Although psoriatic arthritis multiplies everything.) Figuring out how to get it under control — to basically become asymptomatic — is almost the entire battle. It's a disease that for the most part can be kept in check. Since psoriasis is triggered by stress more than anything, staying asymptomatic is a positive feedback loop.
Getting psoriasis under control involves (1) doing an initial intensive treatment to get inflammation down, (2) trying out different regimes, (3) sticking to a fixed routine (topicals, etc.), (3) adjusting until you get last two right. Sticking to a routine also means not skipping topicals when you don't feel like doing it. You'll be rewarded with nice, smooth skin.
For most people, #1 means using a potent corticosteroid. Immune-suppressants (including biologics, which target the immune system responses that trigger psoriasis) are a last-resort kind of deal for people with large amounts of affected skin, since they come with potentially major side effects.
There's no avoiding steroids, but there are a few things that also help:
* Calcipotriene (a synthetic vitamin D3 derivative). Not very potent, but safe. It takes weeks to show any improvement, but it works with long-term, daily use.
* Coal tar works great for a lot of people. Shampoo is particularly great for scalp psoriasis. Comes in both weaker OTC ointments and shampoos (e.g. Neutrogena T/Gel or Pinetarsol), and also a prescription-strength formula that you can rub into the scalp and wear for a week (under a shower cap), and which can clear up the psoriasis completely for months.
* Topical immune-suppressants such as tacrilimus (Protopic) are great for tricky areas like skin folds. Less side effects than steroids.
* UV phototherapy. While a lot of people respond positively, and it's very cheap, it is of limited usefulness, as you quickly reach your maximum dosage, and the effects don't necessarily last that long.
By the way, psoriasis is very often misdiagnosed. To other reading this, if you think you might have psoriasis, get a biopsy to make sure. Doctors are pretty terrible at diagnosing it correctly. Lots of people walk around thinking they have psoriasis when they actually have seborrheic dermatitis, or vice versa.
Lastly, there's a good community on Reddit for this: https://www.reddit.com/r/psoriasis.
Good luck!