Sane and sensible people strategically survey a situation before making their choices.
  If you have any hope of creating a sane and sensible schedule, you need to survey the situation before putting your schedule together.
Once you have surveyed the situation, then you can make choices based on what you see.
  Let's use a metaphor here...
My husband and I often go to special buffets on Thanksgiving and Christmas day.
From experience (and maybe some wisdom) I have learned that before I start loading my plate up at the first station, I walk around the whole place to see what there is and what I might want.
Even if it ALL looks delicious, I can't eat everything and I don't want to fill up on turkey if what I really want is prime rib.
If I want some of the yummy pasta salad, then I don't want to load my plate up with cottage cheese and peaches.
Have you ever had the possibilities for your schedule change - almost right before your eyes?  It's kind of like when you are at a buffet, just when you're about to put something on your plate, you notice that one of the chefs has brought out a steam tray of something that wasn't even available before.
You then change your mind mid-stream because there is a new option available.
And, just like the chef who brings out a new selection that may impact your choices at a buffet, sometimes you get your day, week, or month planned out - and voila, something new gets added to the mix and you have to change your plans.
You have reached a decision point.
The decision point is that place where you either do or don't add something to your schedule.
If you are a glutton for punishment, i.
e.
, having an inordinate amount of appointments, tasks, projects, responsibilities, and other commitments on your plate, then you are probably not making sane and sensible decisions about your schedule.
You are just taking whatever comes your way - from others, from your own head, or from any other source.
To begin to be more sane & sensible, here are some questions to ask when you've reached a decision point:

1. Who is asking?  When you are consciously and carefully putting tasks, appointments, and projects into your schedule, part of the decision-making process should be 'who is asking me to do this?'  You can make decisions based on that person's 'status,' your relationship with the person, whether you like the person or not and so on.
    
2. Why am I being asked?  If you don't know the answer to this question, then ask the "asker.
   "  You can just say, "I'm just wondering, why did you choose me for this?", or whatever other question would be appropriate to ask.
    
3. Does this move me closer or further away from my goals, objectives, values? You, of course, can't answer that question unless you know what your goals, objectives, and values are.
   You need to be clear on what your purposes, intentions, values, and goals are - both professionally and personally - because sometimes, you are asked to add something to your schedule that is out of synch, and adding it to you schedule will NOT be good.
   To stay with the food metaphor, if someone knows that eating shellfish, peanuts, lima beans, or any other particular food is going to make them sick, then putting them on their plate is NOT good.
   Scheduling activities and commitments that can make you, maybe not physically ill, but sick with worry, with stress, with conflicted emotions, and so on, is NOT productive.
   Adding these types of appointment and commitments to your schedule is not being sane and sensible.
    
4. What is the deadline or time frame? There may be items you would like to add to your schedule, but the related deadlines or time frames makes them impossible for you to do.
   For example, if someone wants you to be a guest speaker for a class, and you already have another commitment that day, at that time, then you must say no.
   You can not be in two places at once.
     Likewise, if the deadline for the project is so short that you couldn't possibly (or reasonably) get your part done, then you can't say yes.
   You might be able to say yes to a portion of project though.
     Either way...
   always find out what the deadline or time frame is before you put an item on your schedule.
    
5. Can anything that is currently there be delegated, postponed, deleted, or moved somewhere else?  There will be times that because of the person who asks, the alignment with your goals, and so forth, you will WANT to add something to your schedule even though there is already too much there.
   At this point you will have take a good hard look at your schedule to figure out whether you can move something so that you can make time for this new item.
   If you are adding something that is a high priority, then you will need to move things that are of a lower priority, or delegate them out as much as possible, which is a wise move anyway.
    
6. And finally, the question that you have to ask and answer on a continual basis is: "What do I already have on my plate?"