what are your best tips for decluttering?

[Rizzledizzle]

I need a major declutter and don't know where to start. Can anyone give me any pearls of wisdom?

Don't keep stuff to sell on ebay or car boot sale.

As selling will take hours of your time and you will make peanuts as car boot sale buyers just want extreme bargains and ebay is a pain with the postage etc. And having bags of crap waiting for you to find time to sell it is just another stress you can do without.
Give everything away to tip or charity shop and tell yourself that someone else is gaining from that.
You will quickly forget you ever owned it.

One trick that works for me, is to move stuff to BETTER places. So maybe I don't know whether to keep it or not or the best place for it, but the odds are that many things could be in a better location. Eventually the same type of things congregate and better storage (or disposal) options become easier for me to figure out.