Get up and dressed in the morning. Don't be tempted to stay in your jarmies, it just doesn't work.
From the start discourage friends dropping in during your precious work time, make it clear you must work. I can't tell you the hours I lost when people know you're home and drop in for a coffee.

I was tempted to wait until the kids were in bed at night, but I was often too tired to concentrate by then.

My work hours where a bit funny (which is the whole point I spose). DD would often have a feed about 4-5am, I would find it hard to get back to sleep as I would instantly start listing my tasks, so I just got up then - finish around 8am.
It was amazing the amount and quality of work I could get done. Kids asleep, no phones ringing - everything was so still the time would fly.
I would go back in after lunch and make a couple of phone calls (30 mins) , and Dp would take the kids for an hour between 7-8pm (catch up calls etc).

I managed to spend the full day with the kids, and not be too tired. I was never up much past 9.30-10pm.

I can tell some people would run screaming from the room at the though of being up so early, but it really worked for me.

Other tips - write a task list and stick to it.
Rewrite it at the end of the day so you don't wake up in a cold sweat thinking you have forgotten to do something.
Clean your work area each week, it's amazing how messy you get when the boss isn't around.
Block your time a week or a month ahead. Put in me time, family time, gym time, work time. Stick to it like glue.

It can be hard with kids but they always win in the end so its best to work around them...

good luck with your decision...!