Yes, I would second what Cheekymonkey has said and start with a mid brown.
I would also stick to Clairol Nice n Easy Original until you know what you are doing. Why? Because they are very specific about darkness and tone. Tone is how red/gold or ash/neutral you want your hair. Darkness is well, how dark.
Do you have red tones in strong sunlight, or an indigo hue? Or just a very neutral slightly goldy but not really brown? Try and describe it and I can recommend a shade.
Remember that if the shade you choose isn't dark enough, you can go darker next time or straightaway, but you can't lighten it by using a lighter shade.
Know also that colour builds up. Its like adding another coat of paint to a wall. You need to avoid excessive colour build up or your hair will look black in time. The best way is not to choose too dark a colour, to only do your roots most the time and not run it through every time, buy a tinting brush or be obsessive like me and apply the colour with a foundation brush when doing your roots. (Its really precise and very pleasant to do, you have absolute control)
Always do a strand test. Get a very small piece of hair (maybe 10 strands?) from an under layer of your hair, snip it off, secure it with a sticky label (some people use sticky tape but I find labels better). Mix 1 teaspoon from each bottle in the box together (Clairol are equal parts). Place the hair secured in label over a piece of aluminium foil, paint the colour on to it, then fold up the foil around it like a little packet. Put the little packet somewhere warmish but not in direct sunlight. Why warm? Because your head is warm, and you want a reasonable likeness to the kind of temperature on your head because heat can affect colour development. So you leave it in a warm place for 30 minutes, then rinse the strand and dry it. Look at the strand in daylight, in strong sunlight, and under artificial light, and make sure you like it, that its not too dark, and most importantly that the undertone is pleasant to you - at this point if its too red or just too dark it will be apparent. If this is the case, you need to buy a shade up or a shade less red, etc.