1. Have bins every 100 meters, so you never have to walk 50 to a bin. Therefore no excuses.
2. 2000 baht fines for litterers, with the option of doing two days community service picking up rubbish.
3. Get the tetsabaan to provide street sweepers rather than pocketing the cash.
4. Warn places like 7/11s that if the don't keep their shopfronts litter free they will be fined. If beach umbrella vendors don't keep their area litter free then remove them and replace them with someone who will.
5. Soi 9 theprasitt and many others have truck after truck in late afternoons arriving to dump rubbish by the side of the road. Round them up, make them clean it up ( it is their fault) and if they don't, confiscate their trucks.
One initial massive clean up is required. Bring in the army and let out low risk prisoners of their cells during the day to clean it up.
And education at schools. The schools all sell food out the front at home time. They always leave a filthy mess behind.
If all that doesn't work, then public canings.
Singapore used to be filthy, now it is nearly spotless.
I spend a lot of time in an area of chonburi with a lot of Japanese investment (Don hua roh). It is amazingly litter free where their factories are. Streets tree lined.. They have people sweeping the street daily.