Don't you hate it when you are sitting down to a beautiful dinner, and your shoulder straps keep falling off......
If you are wearing a bra, then you can attach your straps to your bra by using "shoulder stays". In Australia they cost around $6.00 and you hand stitch them to the inside of the shoulder strap. This would not work for spagetti straps, but it will for all other straps.
If you can't buy any shoulder stays, then thin tape and 2 press studs will do the same trick. The bra strap is clipped inside the shoulder stay, ensuring that the strap does not slide off the shoulder
Judith aka genie