Do it as seldom as possible? I hate moving so much. Hmm Start packing as far in advance as you can, always tape up the bottom of your boxes and not just the top, think about how much the box will weigh so don't pack a giant box full of nothing but books, put important stuff you will need to find in a hurry (eg. your glasses, pet food, wallet, keys) into a bag or small box that you stash in your car so well meaning helpers don't pack those things in a random unlabelled box where you won't find them for weeks, label your boxes. If they need to be stored for a while make sure they are properly sealed and it doesn't hurt to throw some lavender or ceder balls in to keep pests away.
That's a good question. If you're happy with the ways things are organised at your house, I'm thinking that putting the contents of each draw/cupboard into one bag/box is a good idea. So, once you get into your new place, you can just put back everything the way it was.
Start saving boxes months ahead if possible. Be ruthless and cull as you pack. Label boxes with rooms of the house to make prioritizing unpacking easy. Don't leave things until the last minute - that's when stress level peak and tensions erupt! If you haven't used something in 12 months, throw it out or give it to a charity.
Being organized is the key. If you start early enough, you can sort your items into things that you need to take and give away. If you can take care of what needs to be given away, I recommend doing it early on so that you can free up space/clutter. On the day of the move, if you are doing it yourself, ask some friends to help out. Start early to anticipate any last minute hiccups. Best is to have movers do it for you (but it costs an arm and a leg).
One large removal company a few years ago now decided to repack some boxes with an extra charge. I had to take them to Small Claims Tribunal because they never advised that the boxes were going to be repacked and there was nothing on the quote to state how boxes should be packed. I won the case. Another time with a different removal company he came to the house and gave me a quote and he got the job. When the removalists came they took one load then came back for the rest and told me it would cost more because the manager only quoted for one load. I phoned him up and they moved the rest of the stuff at no extra charge. I think they were trying to fleece me. I have never had good experiences, the last one moved my brand new bed and ripped the base cover from one side to the other. I will have to move again shortly and will get my son to do it and hire a truck. At least I can trust him.