Nowadays,
1. Poor vinegar into a bottle and spray directly on the glass, then use a soft cloth to wipe the stains
2. You can use toothpaste, corn flour, lemon juice, etc. to remove the stains
3. Use the glass cleaner spray to wipe it
4. Especially, with hard stains, you can buy Putin liquid (Aromatic gasoline) at metal store to clean the glass, the stains will removed quickly
5. Finally, remember to use newspaper or toilet paper to wipe it once again