Pick a brand:
Sometimes it helps to narrow things down by picking a brand. If your workplace already uses a specific brand, talk to the folks who made that decision and ask them why. It often makes a lot of sense to choose the same brand especially, if compatibility is important. Otherwise, do some research on brand satisfaction and find out which brand has a reputation for the factors or features most important to you. By narrowing things down to a specific brand you can often eliminate lots of choices.
Pick a price:
When shopping for electronics there is usually a wide range of pricing. Know your budget before you start. A couple of quick online searches should let you know the range you can expect. When deciding on a budget, pick a price in the middle. Choosing the lowest priced model may not always be the cheapest. Lower costs can be associated with less features, support and lower quality workmanship and materials. Alternatively, highest priced may not mean best, sometimes it just means a particular model is over priced.
Buy the most:
Sometimes people will tell you to pick the features, memory, size, speed, etc. etc., you need and just buy that, but the problem is sometimes we just don't know. Often we are overbuying anyway, simply because we don't know how our needs will change in the future. Also, sometimes we don't know what all those numbers mean. What are megapixels anyway? Ram? Gigs? Clock speed? Hard Drive RPM? Well, when it comes to the numbers here's some advice, more is better. If you aren't sure what all the numbers mean, then pick a price (see above) and then just buy the biggest numbers you can get in your price range. Related to this is advice to buy the biggest and best you can afford. This sometimes doesn't work, which is why at the local youth soccer games, you sometimes see 10 people toting around huge Digital SLR Cameras and multiple lenses. We can often afford much more than we need, but usually, buying the most you can afford means that you will have enough capacity to carry you through the immediate future.
So go ahead, jump right in, pick a brand, or pick a price, and then buy the most.