As with the purchase of any advanced technology, there are a few technical terms that one must be aware of before actually buying it. So if you are going to buy a scanner for the first time then you need to pay heed to following mentioned points.

Bit Depth
A scanner can remember only a certain number of bits for every pixel in an image. That number of bits is known as bit depth. A scanner with high bit depth has more information from which to distinguish between different shades of a colour. As a result a scanner with higher bit depth will produce a good, crisp image.
Scanner with at least 24 bit depth is generally recommended as it is adequate for the most documents and web graphics. If you buy a scanner for slides, negatives or transparencies then you should opt for a bit depth of 30 at least. However, it does not mater much if your monitor and printer can handle 24 bit depth only. Picture scanned on a higher bit depth scanned will definitely reflect better in printouts.

Optical resolution
The measure of dots or pixels per inch (dpi or ppi) is known as optical resolution. Higher is the number of pixels per inch, the better is the resolution and image quality. For an average user, a 300 dpi optical resolution sounds just perfect and 600 dpi is for graphic artist. For slides, negatives, etc. you need the optical resolution of 1200 dpi at least.

Speed
Higher is the resolution of a scanner, longer it will be take for the image to be scanned. Generally it takes around 30seconds for a monochrome 300dpi scan and 100 seconds for a 600 dpi colour scan.

Software
A scanner comes with software also that is generally a basic version of image editing software. To edit the text within your scanned document you will require Optical Recognition Software (OCR). A computer treats a scanned document with text as a picture and not as a text as you think and read. OCR can examine the scanned image and then converts it into a format which is readable by a word processor, spreadsheet or database.
In case you often have to work with images or create different kinds of effects or need to scan and edit text on regular basis, then you must regularly upgrade the software.

Go for online reviews
Web is the best place to know the latest information about scanners. First decide upon the scanner that you want to purchase and then check out for user reviews on the selected models. Based on different reviews of models, you can choose the best deal for your office or home.