Use The Technology
I am a big fan of using the technology that I have in my hand. I mostly shoot in aperture priority (Av) and when I have a specific reason to do so switch to shutter priority (Tv). Generally I let the camera do the rest.
At the 2010PMA Digital Life exhibition there was a presenter who had some of the most amazing macro images I've ever seen. He had a saying he repeated a lot - "use the technology" - the point he was trying to make is that for artistic or other reasons most of the time you should choose either the aperture or shutter speed and let the camera choose the other because today's technology will do a good job. There are times when I will use manual, but generally I shoot in AV unless I want to slow or stop the motion of something then I will set the shutter instead. I usually chimp (review the image and histogram on the LCD) before I move on and will sometimes set either change the exposure value (EV) (force the camera to offset its chosen settings to expose more or less) to get the correct exposure on the area I most want or I will drop into manual and starting from the camera's chosen settings work my way towards the exposure that I want that best matches what I can see.
I find that people who have been in photography a long time and know the ins and outs of their equipment and what it can do often live in the manual world and often insist every photographer they talk to also live in their world.
Film photographers would often live in manual. I usually did because I knew what film I had loaded - the camera only knew the ISO - I knew what it could handle, what range of light and colour and what would happen in different circumstances (well, I like to kid myself that I did - I did get surprises when I was sure something would work and it didn't!).
Today we have a sensor, filters & processor - who knows that sensor better the engineer and embedded software programmer or the chimp (me!) pressing the button on the outside of the box. Generally the answer is going to be the engineer & programmer. However, there are circumstances where manual is going to be better. Off the top of my head:
- back lit subjects - the camera will make a silhouette - I might want more detail in the foreground subject
- bright front lit subjects with an interesting background or even a dark background - you would never see it on auto
- dark (or bright) subjects with patches of bright (or dark) areas and you want something in the middle to capture both.
Full or Partial Manual Focus
I always partially or fully manually focus either by choosing the focus point the camera then automatically uses or just manually setting it with the focus ring. When doing macro I always manually focus and usually set it with live view on 10x to capture the specific element I want in focus then turn off live view and create the image.
There is one important consideration and it is to do with packing up after a session of shooting. During the shoot you might turn on all sorts of things in the camera, perhaps exposure bracketing or you might be in manual or bulb for some exposures after dark. When I am putting my camera into the bag - I usually put my "default" lens back on (24-105 zoom), turn on its image stabiliser and set it to auto focus. On the body I will set the camera to Av, the arpeture to f/8 (otherwise known as the "who cares" arpeture) set the centre most focus point. Additionally I make sure I've turned off things like bracketing and set the EV to the default of zero. This way when that candid or quick moment pops up when you're after a quick snap e.g. family or journalistic moment because you would miss the moment if you had to think the camera is ready to produce the best outcome it can. People who know me also know that sometimes I don't always follow my own advice and watch my reaction when I try to quickly grab a moment during the sunny day with the camera set on a 30 second exposure at f/4. Doh. I've heard of others who simply set their camera to 'P' (Program) so everything is simply on auto when you yank it out of the bag.
What will work best for you? Only you can choose that. Get the camera out and experiment. Then you can choose what you like to work with. You shouldn't do something a particular way because someone tells you to (including this!).