Start by using a wet cloth or T-Bar to wet the entire glass surface. A water/dish soap solution works best. Perhaps some of the dirt comes off during this step but the purpose of this step is not to clean the window but rather wet the window with your soap solution. The dish soap helps to break down the particles that you are trying to remove from the window while lubricating your squeegee motions without leaving streaks.
Step 2 is the longest and most important step, this is where the cleaning happens. Using a rough sponge, scrub the entire surface until smooth. Any stubborn dirt may be scraped off with a razor during this step ONLY IF THE GLASS IS NOT TEMPERED. If a razor is used the glass must be re-wet afterwards.
The most famous tool in a window cleaning arsenal is the squeegee. Although, the act of squeegeeing a piece of glass is not actually cleaning the window, it is simply removing the solution that you have on the glass. This can also be done using a dry towel, the only problem is that a towel will not stay dry... better to save your towel for small spots and edges.
Starting from an uppermost corner, squeegee the solution off moving downwards without leaving any lines or streaks.
Using a completely dry towel, run your finger along the edge of the entire piece of glass. Make sure you are always using a dry portion of the towel as any moisture left on the glass will leave streaks.
Wipe off using a wet rag the outside rim of the screen and netting. Open/Take apart window and remove plastic liner that runs along bottom of the window to vacuum and wipe out track. Once finished replace liner and put window back together.