First, check that your skills are up to date. You may be given a little leeway to let you catch up, but life will be better for you and your employer if you arrive back at work as ready as you can be. Find out in as much detail as possible what skills you're likely to need and then take an honest look at your existing set and work out what's missing. You may need totally new skills and some of your older ones may need updating, so use the time to develop them, either on your own or by doing a short course. Every little bit helps. And if you are going back to your old job, don't presume that your old skills will suffice. Not only may they be rusty, but the technology and processes in that job may well have changed. Be prepared.
Be as informed as you can about the organisation and the people working in it. If you're starting with a new employer, that means getting hold of every source of information available and finding out everything you can about what they do, how they do it and who does what, and digesting that information so that you can become an integral part of your new team in the shortest possible time. If you're coming back to an employer you worked for before, then arrange to meet some of your former colleagues informally, and your boss more formally, beforehand to find out what's new and who's who. The inside information they can give you is invaluable in plugging back into things once you start, and they can also help smooth your way before you begin by dealing with logistical matters and maybe even doing a bit of personal PR for you.
If you are faced with concerns like child care or making allowance for illness or disability, make sure your arrangements are in place in time for when you start work. The last thing you want is to have to disappear in your first week to deal with a child-care emergency at the same time as you're climbing the steep learning curve. The same applies to even apparently simple things like planning your journey to work. Make sure all your systems are well organised in advance, because that means fewer things to worry about at crunch time.
If you are returning to your old organisation, be prepared to change the way you behave towards former colleagues who now have new roles, particularly more senior ones. The relationship you had before may no longer be appropriate, and coming straight in and treating them the way you used to can cause complications. Take their new positions into account, and be sensitive.
