I have had to juggle several business ventures at the same time as well, seems that you put out the biggest fire first but then other aspects will slide. To stay away from this I allocated time for each at the first of my day, addressing issues or whatever was needed for the time allocated, then off to the next. When all the various matters were completed I'd return to the most pressing or most profitable and complete that.
I only took phone calls from those who had my cell phone number, I didn't really take calls until 10:30 or 11:00 am, my wife took calls, I had an answering service and later had staff. Otherwise I'd be on the phone and not getting much done.
I also planned my day as James has pointed out as a routine, you get use to it and jump in without thinking about what you need to line up. Others also get use to what your routine is as well, they don't call you before 11:00 for example as they know you're out of pocket.
I would also plan my time backwards, knowing I had an appointment at 2:00 I estimated the travel time there, when I hade to leave, how much time for the office tasks, what my allocated time needed to start and when I need to be at the office,.....as an example, I think most of us do this, but it may mean having to get up at 5:00.
Sleeep is very important to me, I need at least 6 hours and that may mean not watching the late show. Here you need a routine and stick to it.
As for organization, I had an air traffic control background in the Army and ATC uses flight strips stacked on a rack that slides down representing the next plane to bring in. Each flight strip has boxes with information or meaning when checked. If a box was checked it meant that the weather had been given for example.
I adapted the flight strip system to my RE, on a white board with deals as they came in at the top and a horizontal series of boxes and comments. As a process was completed I checked it off. I could sit at my desk and at a glace tell the current status of any deal.
I imagine that now, with computers you could punch a key and get a matrix of your status, I only used them for word processing, not a techie as everyone here knows. But, if the phone rang and someone asked what was going on, looking up at my board I could immediately begin telling them what had been done and I know that immediate response will have them thinking that I was really on top of it, as if I were working on it at that moment! I could give an answer quicker than turning on my computer or changing a page. It worked for me. :)