Set your goals and agree on what you want out of your business
We all get into business for different reasons -- some to make money, some for lifestyle, some to make their mark on the world. Are you after the "boat, bach and beemer", or after global domination? Ensure you have this conversation before you start out together.
Making sure you are both pointing in the same direction together will stop many headaches over the long term. Take time also to check your goals regularly as your business grows, making sure you are still both on the same journey, as your life circumstances (including children and age) change.
Know the lines
Treat each other with respect - just because it's your "other half" doesn't mean you can be abrupt or shout at them. You would never speak to "James in sales" like that, so why would you speak like that to your spouse? You need to respect each other even more in your relationship, as you will be spending all your time together, both at the office and at home!
Have clear skill boundaries
It's vital to both work to your strengths. Before you start out together, write down each other's skills, and agree on who will do what in the business.
Where there are gaps, you will need to temporarily fill these until the business gets going, then employ someone to take over the responsibilities for your combined weak areas. These areas will only become more stressful as the business grows, creating conflict in your relationship if not properly resourced.
Have a common front
As your business grows, your clients and staff will challenge your relationship and how your work together. However, don't let people split you up into "he said / she said" situations, and (at least on the outside) have a common front. As well as this, certainly don't fight in front of your team or clients.
Be clear and trust each other
Remember that you are both playing for the same team. Too often, important discussions do not take place when they normally would in a non-family partnership. Over time, this can lead to a lack of knowledge-sharing, which can then turn into distrust. This is bad for any relationship.
Tom O'Neil is an award winning business speaker and best-selling international author.