Job-share with someone you communicate well with and have a good working relationship with!
I job shared for over a year very effectively, we both had the same vision for how we wanted to teach and what was important to us, and we planned together. We had update emails over the weekend, left notes for each other, stuck to the plans so each of us knew what the class had already covered and what still neede teaching, ad we were also flexible. We also swapped days sometimes if we needed to, and were both in the school more than we were teaching so there was quite a bit of overlap when we could catch up and chat.
It helped that we liked each other and got on well, we could present a truly united front to the parents too.
I've job shared since 2001. I've had 5 different partner teachers and all but one has worked marvellously.
The key for me was not choosing to work 3 and a half days. That allowed for a lunchtime chat to handover the class to. We kept a book to make important notes in and I've been fb friends so we can message each other for the little things. Even better is to share with someone who is already working in another role in school. I've shared with someone who also did some PPA cover and it meant we were both at school for staff meetings and to plan together.
I love jobsharing. You have to be good at reminding people that no, you can't do that as you aren't there on a particular day.
Same advice- make sure you get on well, try to have a bit of time together each week. We email a fair amount during the week and have time together on Thursdays. It helps that I work 5 days a week, but only teach on 2 1/2 days.
Accept that you will have different approaches to some things and that that is okay as long as the work gets done. I think it is quite good for the students to have a contrasting approach as long as communication between the two adults is good. As someone said above, be rigorous about when you are there and when you're not - don't allow mission creep, or you will find you are full time but receiving a part time salary!