These are some suggestions on how to keep your HCH clean.
I guess the Prius engine can be washed too but I'm not sure.
My car still looks glossy new in spite of parking it outdoors under a carport for over a year, and basically parked on covered dirt/mud.
I'll never claim to be an expert in the field, but this works for me.

Of course these are only suggestions, and please make any comments you might have. I wrote them in perspective of giving directions for someone to wash my own car.
It takes about an hour an a half to complete everything here.

Some notes:
a. I wash it after the rain has passed, the roads have dried up and no forecast of rain for at least 3 days.
If it is forcast to rain for a long time you can always hose the dirt off while the car is still wet from rain. It really does help to keep it cleaner longer.
And yes, I do occasionally stand in the light rain, rinsing my car off.
I suppose it gives the neighbors something to jeer at.
b. I use a separate bucket & tools for washing wheels, wells and the engine. I use a different bucket & tools for washing paint.
c. Tools are cleaned after each use, and mitts are laundered as well.
d. To avoid scratches don’t use any washing mitt or towel that is not 100% cotton.
e. Use real, brand name carwash. Don’t use any other household soap.
f. I wax the car twice a year, in the fall and spring.
g. I wouldn't wash the car if it is about to freeze outside.
h. Don't use shiny interior treatment products. They get nasty after a while and nearly impossible to clean off.
I. Never wash a hot engine. Let it be cool.
J. Last, never wash a hot car. Touch the paint. If it burns, it's too hot.

Items list
1. 100% Cotton towels. Lots of them. I buy them bulk over at Sam's wholesale club. They are perfect- about 10 inches square.
2. Two 4-5 gallon buckets. One labeled "Paint Only" , the other one "Dirty".
3. "L" shaped round brush. I got mine at the dollar store.
4. Drywall brush. These are available at major hardware stores. They come in various sizes but you want the longest one available. Typically they have no handle, other than the back of the brush and is made of pine. They have ~1 inch single row bristles.
5.100% Cotton car wash mitts. Check the label. Synthetic mitts won't "absorb" dirt particles as well and can create microscopic scratches.
Label one mit "Upper", the other one labled "Lower".
6. One bottle brush.
7. One Large synthetic sponge. (About 6x6" on the ends and 10" long)
7. One gallon plastic kitchen bowl.
8. Tire cleaner.
9. Tire "wet" oil.
10. Brand name car wash and wax.

Wheels & tires
Mix up some car wash soap in the "dirty" bucket.
Clean the dry tires with tire cleaner.
Use the "L" shaped round brush to scrub down the tire sidewalls to avoid nuckle scrapes. Rinse the dirt away with a hose.
Use the bucket of soap with the sponge to clean the wheels, lug wells and chrome lugs.
Use a bottle brush to clean the hard to reach areas of the wheels.
Help keep gunk from sticking to the tools by using LOTS of soapy water.
Use the sponge for wheel wells and other nasty areas (But not paint)
After all 4 tires are done, immediately wash out the bucket & tools used.
When you wash the "L" shaped brush, don't expect it to come 100% clean.

Now wash Under the hood & trunk gutters
Mix a fresh batch of soap again in the same "Dirty" bucket.
Open the trunk and wipe out the gutters with the sponge damped in the soap.
Rinsing the soap from the gutters is easy with a slow, directed garden hose.
Open the hood and soap everything that is reachabe with the sponge & bottle brush, then the underside of the hood itself.
I avoid touching the lead-acid battery for its corrosive properties.
Rinse it all off with a garden hose.
When finished, immediately close the hood and hose down the rest of the car to remove any engine residue that splattered on the exterior paint.
Clean your tools.

Exterior Paint
First mix fresh soap in the different bucket labeled "Paint".
One mitt is used for the upper surfaces (roof, hood, trunk lid) the other mitt for the lower, usually dirtier parts like under the door side bumper guards.
Wash the top areas first and work your way down.
Wash in sections (Roof & glass, then hood & trunk, then sides etc) and don't let the soap dry before rinsing.
Always wipe front to rear to avoid swirls and wash the upper parts first, working your way down.
Stubborn areas like tar or bugs will wipe out with a damp rag and car wax.
When finished toss the dirty water and rinse the bucket out.

Mix up a fresh brew of car wash in the "Dirty" bucket, then open all 4 doors and use the synthetic sponge on the lower & side door jams, avoiding the plastic thresholds.
You can close the back doors to gain easier access to its hinge areas.
The soap can be rinsed with the hose set to a slow & directed spray to avoid wetting the interior.
If it is time to wash the interior then keep the slightly used bucket of wash handy.

If the car is left to air dry you’ll get potentially paint damaging spots so dry the car using cotton towels (bought in bulk at Sam's) or a shammy,

After the windows are wiped dry go over them with windex glass cleaner.
Every 4-5 washings I'll apply rain-x to the exterior glass.

Interior
Notes:
a. I don’t eat, or let others eat in my car.
b. I don't drink anything other than water in the car.
c. I'll vacume every 2nd-3rd exterior wash or as needed.
d. I'll wash the interior plastic parts every 10K or if spots, smudges or other nasties are seen.

First remove all mats from the car, set them out on the driveway and evenly pour 1/2 of the bucket of wash (saved from cleaning the door jams) over the carpeted mats and let them soak.
Cover the dash with cotton towels to protect it from overspray, then spray down the windshield inside surface with windex, then wipe the glass down.
Clean the glass a 2nd time with a fresh clean towel.
I go over it again with Brillianize, a glass polish.
Remove the towels from the dash and use a vacume with a soft dusting brush attachment to remove the loose dust off of every plastic interior part of the car.

Get the clean plastic bowl from the kitchen (sorry dear) and a fresh, clean cotton towel. I'll fill the bowl with warm, clean clear water.
Wipe every interior plastic part using the towel that is dampened with the water, no products added to the water or the surfaces being cleaned.

Change the water when it gets cloudy, there is no soap in it to "hide" the dirt.

If the wiping is left to dry on its own, some smooth surfaces (Chrome shift bezel, radio console etc) will streak before it dries, so wipe it dry it with a fresh towel.

Vacume the carpet, especially the edges where dirt drops off the edge of the mats, then change attatchments to an apulstry brush and do everything else, including door fabric and the trunk carpet.
The rear seat head rests are removable for cleaning the rear deck & window.
If the damp cotton towel used earlier had left "towel specs" on the dashboard then now is a handy time to switch attachments and vacume it one final time.

Now that the mats have been soaking, pour the rest of the car wash soap bucket on them and scrub them down with the drywall brush.
Hose them clean and hang them up to dry.

If the tires are still wet from washing then dry them.
Spray non-wipe tire oil to the sidewalls.
Since some of the oil will overspray onto the metal rims, take a clean towel and wipe the rims down. The oil will spread out and won't catch dirt so easily, and the oil will make the rims nice and shiny. Don't forget to wipe around the chrome lug nuts.
With the same slightly oiled rag, wipe down the headlight covers and tail lights.

Reinstall the mats when they are dry and you have a beautifully clean car.

Keep doing this as soon as it is neccessary and it will stay this way for a long, long time. Don't "let it go".

Every other day or so I'll use a spray on product for the paint like Dupont's "Armor shield" that is specifically made for protecting car paint.
It keeps the surface wax-like smooth.
(No, NOT Armor-all !)

Efficient drivers do it better.
1003 miles a tank personal record. 74MPG calculated. HCH1 CVT