At first, don't start immediately by checking my portfolio because it will not add to my credibility. I am still beginner here on DT.
But... I have some tips which may theoretically give some ideas on shooting objects closeups.
Some some of this tips will differ depending on equipment you have. I may miss some tips though.
I think that isolated objects on white can be a good sellers so I want to give it a try. Still experimenting and improving and I really hope that I in time will have much more of those in my portfolio.
One of the greatest issues in this matter is good isolation. Although there are many tips on how to achieve isolation using your graphic software, I am sure that there are photographers who can make it perfect even without using software. They are more experienced then me and probably have better equipment and shooting setup. Lets cover few aspects on it, in case you cannot afford professional studio equipment, but you have descent SLR camera. I personally use Olympus E-510.
Camera and lenses
I cant say which camera is better for shooting objects closeup. General rule may be: as good as possible. Since you may sell your image for designers who don't need high resolution prints, I guess that even 6Mp camera can be good. I am not expert at lenses too but someone may have some good knowledge about what focal lengths works best for the purpose.. Since this article is closely about sharpness, consider not using to "long" lenses, for the matter of stability as we will see later. I like to use my 14-42 ZUIKO at around 35mm even it is not that fast (1:3.5-5.6). Lenses with bigger aperture (like 1:2.0) will have advantage in demands for light and will make easier to set your small studio. Anyhow, you will use the best you could.
Small home studio
You may find many ideas for cheap and small home studio if you search on Google. But here are the basics. Buy yourself large sheet of white paper (or some similar flexible material). Try to find the whitest you can, because not all white is actually white. This will be used as your background. Lay the closer part of the sheet on the table and fix the farther part to the wall behind table or to some rack, so you get the sheet hanging down from it and going towards you to your horizontal stand in a slight curve. This will cause lack of any corners behind you object. This is your shooting stage. The best option is to have a steady tripod to put your camera on. You can improvise by putting camera to lay on some other stand if you can set your direction well. Fixed camera position is one of demands to achieve stability of your lens which directly affects the sharpness. The tripod is the best thing which assures no flaws and make camera operating the easiest possible.
Lighting and shadows
Lighting is the biggest problem. It directly affects your image sharpness. Poor lighting asks for wider aperture opens which decreases sharpness. You should go for the strong lighting. I bought two 500W lights (even I think it is not enough). Those lights are somehow pointed which causes harsh shadows and specular highlights reflections. To avoid this you need to make lighting diffused bi putting some translucent material on front of it. White plexy-glass could work fine, and even a sheet of white silk (umbrella perhaps). Note that this will lower your light strength a bit but you will loose specular highlight reflections and harsh shadows. Try to position your lights from front top left and right. Look for the setup where two shadows will nullify each other the best. With this basic setup you can give it a try. There is probability that you may use even remote flash light at some point for a final touch. I wish I could have one.
With this basic stage setup, you can do several more things in your camera setup to achieve the best possible image. Depending on your lighting you can set small aperture open. I think that for sharpness you tend to use the smaller open possible. But, some sources claims that it is good to avoid two minimum opens (which varies from lenses to lenses) because of lens characteristics so keep that in mind when experimenting your best setup.
Many says that the widest open which will do the descent sharpness is 8. If your measuring shows bellow that then your lighting is probably to poor. Truth is that since we work from stable position, we can compensate this with longer shooter speed, but that is improvisation since the edges of the object on white are the most sensitive area. Also have in mind that your exposure time is best to be at least twice as is your focal length (35mm equivalent). If you shoot with 40mm digital it is about 60-80mm equivalent (depending on your sensor ratio) so you shouldn't go bellow 1/160. There are exceptions if you can use fill remote flash, but that is another theory. Anyhow go as fast as you can with the smallest aperture you can. And yes ISO should be the lowest possible, usually it is 100, even some have values of 50. Highest ISO, more noise. Any king of noise will probably get your image rejected.
So, now hou have good background, small aperture, fast shooter speed and good lightning, your object doesn't have any specular reflections and very little smooth shadows around base (if any).
Ready to shoot? Not yet, there is some more...
To further improve your chances to get sharp image you can check your camera features to see if there are another options which can help. Lets name a few.
Image stabilization - While it is practical if you shoot hand held, no matter if stabilization is built in your camera body or in your lenses, I prefer to have IS off for this kind of shoots. Shooting from tripod with no hurry doesn't demand IS, but IS will probably try to do something. It is absolutely safe to turn it off. Try it both ways and see the results, then decide.
Mirror up or anti-shock - this feature have different names on different cameras. Check your manual. You a looking for feature which actually raises the mirror of your DSLR and give some delay before the shoot is taken. Purpose of this is to avoid micro vibration caused by mirror lifting. The delay can be set different values, usually 1-2 seconds are good enough.
Focusing - Some cameras have absolutely perfect auto focusing, you can give it a try. Some have problem with manual focusing because of small viewfinder. The best would be use manual. My E-510 have handy function of Live-view. Check if your camera have this. This feature lifts the mirror allowing you to see live image. You can zoom this image up to 10 times, so you can clearly see the edges of a detail, and then perform manual focusing, exit the live view and shoot away. Don't have live view open too long time as it heats the sensor.
Remote or delayed triggering - Your camera may have remote IR trigger so it is good to use it. It allows you to keep your hands away from camera and avoid shake during pressing your shooter. If you don't have remote, use your delay timer. Mostly they have 2 or 10 seconds delay. Two will be enough. Delayed triggering in combination with mirror-up is a great help. Those delays allows camera to become steady after you press the trigger and mirror lifts up.
Noise reduction - Every camera has some noise reduction if you shoot JPG. I prefer to shoot raw because it allows to inspect and develop the image later. If you cantt shoot raw then you should experiment with your camera considering noise reduction. Algorithms are different and it is not easy to predict results. Noise reduction could remove some details on your image , specially on edges, you feel free to check your best setup. if you gave everything fine with noise reduction off, switch it off.
Depth of field - you may find a problem with depth of field. If your lenses at current setup produces shallow DOF, your object will not be entirely in focus. Depending on object it sometimes works. If don't, try to see if you can do a different setup so you get deeper DOF. If not then you can use multiple images with different focus which you can stack later in special software like Adobe Bridge or Photoshop to get all focused area together.
Ok, folks, thats all i have to say. Please don't judge me to hard, I am amateur and still struggling with practices mentioned above (as you can see by the image included). I'll be glad if some of this ideas help you to find your way to produce better photos.