A few points: As Bod says, if water is escaping at the top of the squeegee, you might be "leaning back". The upper end of the blade must be ahead of the lower. In that way all the water is directed down the glass. If you have the squeegee blade vertical, or leaning back, water will run up it and over the top.
As to technique, I always teach that you should place the blade on the glass near the top and in the middle of the pane. Then (with the top end leading) sweep up to the top frame and match the direction of the stroke to the edge of the window (to avoid hitting the frame which will cause a jump and leave a mark). Sweep across to the corner at an angle of 45 degrees until the leading edge of the blade reaches the corner. Bring the squeegee smoothly to a stop and without changing the angle of the blade start bringing the squeegee down the side till you reach the bottom. On the way down smoothly change the angle so you arrive at the bottom corner with the blade at 45 degrees with the leading end lowest (into the corner). Sweep a short distance across the bottom and then up to where you started at the top, turning the blade as you go so that you arrive at the top edge, just before the bit youve already done with the squeegee angled the opposite way.
Repeat as above into the other corner and then down. Now you have cleared three sides of the pane. The "lump" left in the middle is easy to do as you dont have to worry about doing the edges, just sweep across and back, always keeping the leading end of the blade in front, and work down the glass to the bottom.
Squeegee rubbers contain "volatiles" - solvents which will evaporate and leave the rubber brittle. This will cause tiny cracks in the edge. Rubbers should always be stored in air tight bags to prevent this. If your supplier has them in boxes out in the open on display, they can quickly deteriorate, especially in centrally heated showrooms etc.
I once returned a consignment to Ettore because all my men were complaining they left streaks. Ettore sent me some new ones, and they were perfect.
Now I only buy from the bigger suppliers (Cleantech, WC Warehouse, The Fed etc) as hopefully their stock turnaround is shorter so rubbers arent lying around on shelves for months on end and drying out.