Step 1: Snail and slug removal
The most effective (and green) way of getting rid of snails and slugs is hand picking them from your garden... Yes, I know that sounds like a disgusting job to do, but it is much better than killing the wildlife with pesticides.
If you never have done snail and slug picking, be prepared for the shock of how many snails and slugs that lives in your garden (when I first started doing snail and slug picking, I was amazed how many snails and slugs that lives in my garden, there was like hundred's of them)!
Through my experience of snail and slug picking, the best ever time to pick them is a few hours after sunset after a rainstorm although some snails and slugs come out at night or in a rainstorm during the day.
The reason the snails and slugs like to come out at night is because it is cool, fewer predators, and less chance of drying out, if the snails and slugs are out in a sunny day, they would get too hot and dry out and die.
When you go snail and slug picking, put the captured victims in a bucket with some soapy water so they cannot climb out of the bucket while you are doing snail and slug picking, and put the lid on after you are finnish picking them, otherwise they will try get out of the bucket. Also if you are squeamish about the slime, wear rubber gloves or use a long-handled dandelion digger or a pair of long tweezers.