I'm planning on having extreme hair coloring in about a year, and that will require serious bleaching first. Are there products I should be using on the hair this year in preparation? Should I be sleeping in a bowl of coconut oil every night? Argan/Moroccan oil on the whole head after every shampoo? Drinking 3 gallons of water per day?
I've only had my hair lightened (2 steps) once, decades ago, and we didn't have the products available now. So, I'm looking for: what has worked for you or your clients' hair before and after.
Though completely aware that I'm going to experience breakage & loss, anything I can do to lessen that loss before & after is worth a shot.

depends mostly on the type of hair first of all. fine, thin hair requires much more care. thick hair takes it better.

had one model that was totally fried by over processing. yes, keeping the hair health is the important factor before you start. but it's a multi-step process. besides the conditioning, it needs to be left alone - no other bleaching no coloring before hand. maybe needs month or three depending on the length of the hair. during that time, conditioning and air drying when possible, again depending on the type of hair.

next, it also requires attention when you do the actual coloring. processing only to the correct point and stopping the action. that takes knowledge and experience. a great colorist is very important. if the hair is too thin and/or not in good condition, the colorist should simply refuse to do it. no matter how much care before hand, bad processing will still kill the hair. a good colorist will value the hair more than the final color.

takes someone who understands hair, has lots of experience and who cares - not just anyone with a license, a shop and claims to be good. no matter what you do - it depends on the colorist.

Everyone is different.  My daughter had her hair bleached once and got chemical burns on her scalp. 

Go to your salon , ask the colorist these questions.  Get a skin test done first.

Find a salon that uses Olaplex. Olaplex is a new technology--it's a treatment that protects/repairs hair and reduces the damage chemical processes inflict on hair.

It can also be used as a stand-alone treatment to repair the broken disulfide bonds in damaged hair after bleaching.

I used Olaplex on my hair for every process when taking it to white-blonde

Deep condition your hair at least once a week, regardless of hair condition. I like Kerastase's MasqueIntense.

I second the recommendation above for Olaplex. This is something that is done at the salon while they work on your hair.

You need to use a shampoo specifically for blondes; a purple shampoo that keeps your hair from going brassy. My favorite is Paul Mitchell's Forever Blonde. My second would be Blonda by Unite, if you don't mind the grape Jolly Rancher scent. Condition every wash with Paul Mitchell Awapuhi Keratin Treatment and Bumble and Bumble's Quenching Conditioner, alternating each time. Keep up with the MasqueIntense every week. *But* wash your hair as little as possible when this blonde.

After each wash, dry hair with a soft old cotton tee shirt. The hair is too fragile for towels. Spray with Unite's 7 Seconds, then Paul Mitchell's Forever Blonde spray to preserve the color. 7 Seconds detangles, conditions, and protects from heat tools, sun, chlorine, etc. Comb through with a wide tooth comb.

Use heat tools as little as possible. When you do, use the lower heat settings.

Thank you; I really appreciate the advice! Currently, my mane is dark brown with scatterings of gray...most of it almost to the knees, bangs about a foot long, previously shaved back about a foot long. By year's end, hopefully the shorter stuff will be at least to small of back. But, no coloring, no bleaching, no hair dryers; always air drying.
I realize I won't be able to keep the length & the white forever, but this is a "turning 60" thing & worth having to cut it all off in a very short few years.
I'll start doing the deep conditioning now & start looking for a local salon. Luckily, I've already been given the business cards to 2 possible places, so there is where I'll begin.

deep conditioning treatments are important but be careful with moroccan oil. Silicone based oils can cause buildup on the hair shaft leaving you with the orange tinge that it is most defining with moroccan oil. Coconut oil is fine to use before bleaching however once you lighten i would not recommend doing coconut oil treatments for a good amount of time after as it is most alkaline than hair which actually causes the hair cuticle to open up (losing that beautiful blonde finish and leaving you with the yellow brassy pigment that is the base for blonde hair)

Thank you, Brittany, I had worried about the possibilities of the brassiness associated with that type. Trying to avoid the silicone oils for hair; they seem to build up too much. Is my Moroccan/Argan oil generally mixed with silicone base, that you know of?

Look at the Guy Tang hair channel

https://www.youtube.com/user/GuyTangHair

https://www.youtube.com/watch?v=hCNBEaPCuj0

How to Fix Brassy or Orange Hair
https://www.youtube.com/watch?v=SSAZFlaQ51U

Another option is doing hi-lights and adding more every 6-8 weeks after u have gotten the initial hi-lights. I do suggest olaplex it is an amazing product but it is also not a "FIXER." It is to basically to not shock your hair if you wanted to go to a platinum blonde all at once. It definitely does help but if some ones hair is already damaged there is not much it can do. Deep conditioning treatments are also a great thing to do once a week. Making sure you are using good shampoo and conditioner as well as styling products. Make sure to ask your stylist about all of this and what they suggest. I can make suggestions but thing is I like to physically touch a persons hair and look at it to see what would work best for you.

Olaplex! And pre treating hair with coconut oil the night before and arriving at salon with it still in hair is great! Remember it is a process and you get what you pay for. If you have a specific date in mind you want your hair completed- start sooner- it may take 2-3 sessions to get your desired result.

I read all of your suggestions, researched the daylights out of each one, checked out stylists in the Tampa Bay area, drank gallons of water to keep skin & hair hydrated all year.
I DID IT! Regarding chem burns on scalp; we stuck with black at the roots instead, so that touchups only require black dye. 6 pots of color made my hair beautiful & I think it finally looks like ME.
Now, my learning curve is about curling irons, flat irons, etc. Try to make this bleached & dyed hair look like it did when I left the salon, smooth & shiny, instead of a multicolored pouf.
We'll do the monthly dyeing till the color really soaks in, then monthly glazes & touchups.
All hail hair stylists!