Actually, flash can help enormously if you underexpose for ambient and rely exclusively on the flash for your lighting. That would be quite typical for some types of studio shooting, or other creative shooting scenarios. You can shoot at 1/125 and still not see shake/blur, if you exclude ambient light.
This is a 2 second exposure, with flash. Is it sharp enough?
Without flash (or possibly with)....
- you need a shutter speed (or flash duration) fast enough to eliminate camera shake;
- you need a shutter speed (or flash duration) fast enough to eliminate subject blur;
- if you have IS then be sure to give it time to spin up and stabilise before releasing the shutter;
- you need accurate focusing and/or sufficient DOF to conceal small focus errors;
- depending on your DOF you may or may not be able to use focus/recompose;
- with a soft lens, especially a zoom, you may want to stop down to improve lens IQ;
- but you don't want to stop down so far that diffraction causes more harm than good;
- contrasty light, from the side, will create more detail in texture and improve the impression of sharpness;
- soft lighting from the front will reduce/eliminate visible shadows and will conceal detail, making things look softer;
- the more you fill the frame the more detail you will capture and the less enlargement you will need to apply. The shot will look sharper and more detailed;
- the smaller your subect in the frame, and the more you need to crop, the less detail you will capture, and additional enlargement will increase the visibility of flaws in the capture;
- the higher your ISO the more noise you will have, perhaps requiring more NR, and consequently softening the image;
- the smaller your enlargement the less critical your sharpness needs to be. the larger your enlargement the more precise everything must be.
Those are probably the main points. So all you really need is the right lighting, the right focusing, the right shutter speed, the right ISO, the right aperture, a model that doesn't move too quickly, and a steady hand. What is "right" depends on the subject and scene you are dealing with, and how it is lit. Balance those things correctly and you should get sharp results.
Once the capture part is over with it then comes down to skillfull processing to make the most of the image captured. That is an art in itself.
p.s. if you think a tripod may be too cumbersome, how about a monopod?
EDIT : Just seen your post with the example. For a shot like that I would say that f/8 would be a good starting point, and as there is no subject movement to speak of you only need a shutter speed sufficient to combat camera shake. I don't know what your max sync speed is but I would suggest trying a shutter speed of around 1/200 or 1/250 and 200 ISO. The problem then is whether you have enough light for the scene. If you are relying on natural light and it's anything like the grey old day here today you will run into problems. Bounced or off camera flash might well be your best solution. If not, you'll just have to compromise on one or more of the exposure controls until your exposure is good. If you shoot with the 50mm then unless you really need bags of DOF you may be better off opening up to something like f/2.8 and then seeing where you stand. A tripod or monopod could let you relax your shutter speed too, and you can always bump up the ISO if you need to. It's really hard to give definitive answers without seeing the scene and the lighting. FWIW, depending upontoday's overcast daylight alone, I would need 1/15 at f/2.8 and 1600 ISO. Not good.
