You need to see the picture first. Only then can you make the decision of how to render it.
When you are out shooting, it is far better to come home with two good pictures than a whole card full of crud. You might stumble across the odd good picture by chance. Most pictures are seen before they occur, so you can then set up to record the scene as you want. MAKE PICTURES, don't TAKE pictures.
Aperture Priority will work for shutter speed requirments as well - it is easy. f2.8 end of the aperture scale will give you the fastest shutter speeds you have. f 16 end will give you the slower ones.
EG: shooting moving motorcycles (not necessarily motorsport), maybe in traffic. You want to blur the background, you are going to have a slowish shutter speed. You know this is going to come stopped further down than where you are now (take a peek through the finder at whatever the thing is set on and look at the numbers - you now have a good idea of where on the APERTURE scale your required shutter speed sits - YES, I did mean to write that.
Say, you peek through and see 1/800 at f2.8 - OK you immediately know that to get blur in a picture you are going ot be down around f11, that will give you 1/60 f11, or thereabouts. So one click either side is going to be abou right.
You want action stiopping speed - you going to have to stay open. Depth of Field is what it is for the desired settings. You can't, I am afraid, have a slow shutter speed AND no depth of field, unless you are shooting macro of course! Slow shutters means big F numbers, and the corresponding depth of field.....when panning this doesn't matter though because you are seperating your subject with blur. The subject stays sharp, the background efinition is lost by the motion blur, so your subject jumps out of the shot as the one part that is "sharp".
You want fast shutter, sorry depth of field goes out the window!
I would not use film speed to alter things myself, not from choice, only from necessity. For 20 odd years I shot motorsport and other action stuff on Velvia (50 asa for those who don't know), even with a 500mm lens. You were limited. So you had to seek out those parts of the circuit that had light. It was a good grounding. If it was dull, or worse, wet, we did resort RESORT I said, to Fuji 100 pushed a stop (200) - it had to be really, really dreadful to go as high as 400. To the point you would only shoot if you had pages hanging on the backof it, because you knew the colours would be muddy at that film speed. No contrast, spray everywhere, water dripping down your neck, a chamois in every pocket! And GRAIN, where you didn't want it - 400 tranny film was quite grainy. Not what was wanted.
Anyway, the reason I mention this is because if you learn to shoot at 100, keep it there unless you really, really have to go up a click. 100 is fine for wheelying bikes even under full cloud - you just need to be wide open and follow accurately. You take the shots the conditions ALLOW you to take. Think of what you have got - not what you would like to have. If you have some light, then the world is your oyster. If you haven't got any - you are limited.
.. I see it before it happends ...My cameras up to my eye... Just a few seconds to go now.....I can see my cameras set on f2.8 through the view finder, loads of speed, so I dial back some focus range to f8 with a quick rotate of the dial, still enough speed left to prevent any bluring, the reflections will be the same focal lenght as the shop window so no problem.... last seconds, shes just entering my framed window from the right... ready 'click' .... Oh b****r! a big truck just pulled into my view and I have nothing but a great grey smudge... the jam starts moving, the girls gone ....Hayho
