If you want the best sea glass in the world, Seaham England is the place to be! This year I went there twice. In March after a storm with my 2 of my friends and in November with my cousin Barbara form Florida (who is a glass collector too). Both times we stayed in the same nice house which was close the the beach, the supermarket and the pub. The walk to the cliff where the good glass can be found is about a 20 minutes walk. Make sure you are there at low tide and be there first.
Where to look
The best way to find glass is to walk up and down the pebble bed. If you walk fast you can find the big round ones and if you walk slow and take your time you can find lots of small ones even multi colored ones. The colors you find most will be green and white but if you are lucky you can find lovely blue and red ones, or even pink. And check out the black pebbles by putting them on the light of you phone. You will be amazed how any of these pebbles turn out to be made of glass and show their hidden colors.
When to go
The best time to go is after a storm from the east, then the ocean will bring more rare colors ashore. Unfortunately when you do not live close to Seaham and you have to plan your trip ahead this will not always be possible. But even then there will be enough glass you can find. Spring and autumn will be good seasons to go, since there might be more change of stormy weather and it is not yet so col your hands will freeze off.