I paid for part of my post graduate coursework washing windows professionally.  I was cheaper than anyone else, and got angry calls from competitors!  LOL

It's cheap to start up and another fellow window washer put himself through a private university doing the same thing.  It's very good money, but labor intensive, of course.  Later you can hire help, and work at getting monthly contracts.  Always keep the names of your customers and mail them reminders four times a year, or just before a holiday.

My friend gave me these tips for starting out:  You can google "window washing tools" and get TONS of great information, too.

Tools:

A small truck, OR a small trailer that can hold a 20' ladder.

Light duty, 20' extension ladder for 2nd story windows (with stabilizer "arms" for additional safety)

4' light aluminum step ladder (I emphasize light because you'll be moving this around a lot)

2 five gallon buckets (one spare)

15 clean, old towels to place on sliding door thresholds and window sills during cleaning to catch spills.

Window Cleaner Custom Mix:

In a five gallon bucket combine 1/4 cup of Acetone with 1/4 cup of denatured alcohol with 3-4 gallons of clean water.

Add 2-3 drops of Dawn dish-washing liquid (just enough to break the surface tension on the glass, but not enough to heavily sudz up, or leave streaks)

Use the largest squeegees that will fit the smallest areas of glass you are cleaning.

I maintained 3 rubber squeegies:  6", 12", 18"

2 extension pole/handles (one for squeegees, and one for the lambs wool applicator for large windows.

1 lambs wood applicator for large windows. (make sure applicator isn't larger than the mouth of the bucket (or get larger container for cleaning solution)

1 hand-size sponge for applying cleaner to standard windows.

1 palm-sized sponge.

1 squeegee holster

Cleaning windows the fast way:

Place towels on the window sill and on the floor below to catch most water/drips, etc.

Dip either hand sponge, or lambs wood applicator in bucket filled with cleaning solution, and wring sponge until it doesn't drip, but not "dry".  The applicator may drip since there's no practical way to squeeze it dry.

Wipe window (scrub wheere necessary).  "Smokers" windows will need two applications to loosen smoke residdue.

Use rubber squeegee to clean from top down.  Experiment with one single wiping motion, so you're not having to lift the squeegee from the glass more than a couple of times and wiping the blade before placing the squeegee back on the glass.

Use clean paper towels (these don't go very far), or clean, cloth towels to wipe the corners of the glass and the sills as necessary.

It's best to remove all screens first, then clean windows.  Otherwise, the screens can get the windows all dirty again.

After the inside has been done, do the outside.  Of course sometimes it's easier to do 2nd story windows from the inside, and sometime removing the sliding windows make them easier to clean.  Just be sure to put towels down to catch the dirty water so you don't soil the carpeting.

NOTE:  This is a sales and marketing job!   You can charge extra for using a "razor" to remove bug stains, and marks.  You can charge extra for cleaning the crevices and tracks in the windows.  You can charge extra for washing the screens, and even charge extra for repairing screens.  Also, you can consider getting a referral fee for getting windows repaired by your local glass repair contractor.  Or charging 10% more than the costs of repairing the window in return for getting it repaired for the customer.  Elderly customers love this!  In fact elderly customer like the attention to detail and are often willing to have you do the "works".

If people ask if you're bonded or licensed, you're charging too much at the beginning.  Under-bid at the beginning and then up-sell additional services like crazy.  BTW, you're there originally ONLY to clean the glass.  "Razoring", screen cleaning, crevice cleaning, track cleaning are ALL extra.

Get written testimonials about how "great" your services were, how friendly, etc. and put them in a leather binder to show prospective customers.  With a dozen testimonials in your "credential book" many customers will HAVE to have YOU do their windows.  Word travels fast if you over-serve your customers and make them feel they "stole your services".  Later you can relax once you've got sufficient repeat and referral customers.  This will only take a few weeks to accomplish, but be patient.

Once you get too many referrals and business to do yourself, hire some help, train them and give them a % of the business so they'll stay with you, and not eventually "compete" with you.

Also, always work to get long term contracts with businesses.  This will be your lifeblood, and you may abandon residential referrals after a while.  That would be a nice choice to have!

I think this was godsend to me when I was a starving post-graduate student!

Have fun!

What to charge?  If you charge $10 dollars a window (the whole window), you get all the work you want, I'm sure.   Then if you up-sell all the remaining services you should be somewhere in the ballpark of $20 per window.  You can find out what the competition wants by asking them to bid your own home!  HA!  Do what works.  Don't get greedy, but up-sell 'til the customer says, "no."

Go for it!