Getting into a terrible tangle is every knitter's nightmare but I find the best way to keep knitting tangle-free is using a yarn bowl. These are specifically made ceramic bowls with a clever little slot perfect for the yarn to glide through whilst you're knitting.
I love MaidOfClay bowls on Etsy, they come in various colours and can be personalised with your own name. And if you're like me and knit on the go, my travel version of a yarn bowl is an Ikea zip bag with a hole cut in one corner to thread the working yarn through. That way, there's less likelihood of the yarn getting everywhere in your handbag and getting tangled with your keys or purse.
But of course, never be afraid to cut the yarn if it gets too disastrous or you'll spend more time de-tangling than knitting!