No mentor?! First things first... you need to get that fixed!

Your mentor will be able to help you WAY more than any of us will. I see you live in MO - I know there's a big Sheltie community in that state.
I'm certainly not the know-all of show grooming, and hopefully someone else can chime in and correct the details I've omitted or gotten wrong, but here's the basic routine for the week leading up to the show:
Sunday-Wednesday: Dog runs around in the yard, getting filthy.
Thursday: Evaluate dog's cleanliness. Does the dog (a) need a full-body bath, or (b) just the white parts washed?
IF A:
Thursday: Brush dog out completely. Line-comb to the skin. Pull out every bit of thatch/dead hair. Bathe dog, with special attention to the white parts. Towel dog...and brush, and brush, and brush, until the dog is dry. Trim head, ears, feet.
Friday: Try to keep dog clean by keeping in a gravel run. Re-bathe whites if necessary.
IF B:
Thursday: Dog continues to run around in the yard, per the usual.
Friday: Brush dog out completely. Wash white parts. Towel dry. Trim head, ears, and feet.
Saturday is dog show day.
- Continue to try to keep the whites clean.
- Drive to the dog show.
- Wash whites in a bucket, if necessary. Wash whole front with spray-n-wash, if the dog puked all over him/herself. Towel dry.
- Brush the dog again with water.
- Do any additional trimming necessary (trimming is never really done... you'll see new things in new light, and the hair does grow).
- Prep for chalk: Cholesterol on the legs, light cholesterol on the ruff, an even lighter type of cholesterol on the face. Brush all "greased" parts to open the hair and work the product in.
- Chalk: Stiff brush, in against the hair on the legs. Use baby powder (probably) on the ruff, brush in. Pack white chalk into face and layer colored chalk on top. Finish with white block on any white facial markings.
(are you getting tired yet?)
- Brush the chalk out of legs, ruff, and face - but not too much out.
- Fret about the ruff. Is it standing up? Is it standing up enough? Add some more product. Add some product that the lady grooming down the row from you is using. Add some of that product the guy at Cherrybrook said works great.
Time to go to the ring: bring a pinbrush, greyhound comb, and a spraybottle of water (nothing else, just water).
- Mist your dog down lightly. Brush. Repeat until it becomes a neurotic, self-calming ritual. Your dog will look grand (but will probably think you're nuts).
- Enter the ring. Continue to mist and brush when the judge isn't looking.
Sunday (Another dog show! You're not tired yet, are you?)
- Repeat as for Saturday, but evaluate whether the dog needs a going-over with spray-n-wash first, to give you a clean slate.
NB: Any and all of this can and will vary with
the weather,
the dog,
the dog's age, sex, markings, coloration,
the judge's preference about product,
the judge's nationality, and
the lighting where the dog will be shown.
Oh, and if it's puppy, add in some time to take ears down Saturday morning and put them back in again Sunday afternoon.
Sunday evening: Go home. Turn the dog out in the yard. Repeat.
Now... there are so many nuances and details here. You need to figure out everything from what products to use to how much chalk is too much chalk to how to actually trim a dog's head (it's really an art!). It isn't really something that you can learn online... I had the benefit of going to many shows with my mom, working for several years assisting a Collie handler, and getting instruction from talented people who were kind enough to give my mom and I tips. It takes time, and it takes practice, and it takes hands-on help from mentors, but you'll get there.