In figuring out this process I relied on this thread: http://www.homebrewtalk.com/f12/20-lb-sugar-jar-yeast-nutrient-114837/ which provides a wealth of knowledge and specific processes. You will find some other resources out there that talk about using acids for this same process. I actually use acid myself. It produces a slightly different process and product than that thread but at a minimum the thread gives a good explanation of what you will make.
For this process I am only going to convert half a pound of sugar. It is important to note that when you make syrup you are adding water, which adds weight, so when you calculate the syrup addition in your recipe you need to account for the weight of the sugar not the syrup.
For half a pound I am going to add half a tablespoon of lemon juice and stir well to get it blended.
The heat should stay on medium until the very end, if it is ever raised. Although it is a slow process doing all this boiling on medium you don't want the sugar to get too hot too fast or it will scorch and taste burnt.
Once you have everything mixed up it's a fairly simple process. Let it boil. It will start to thicken and change colors as it progresses. You want to add a spoonful of water to it as it starts to get too hot or too dry. If you have a candy thermometer you can keep it at the right temperatures (270-290F) by adding water but if you don't you will basically want to make your best guesses. If you end up adding too much water it will still turn out ok, you will just have to take into consideration in your recipe that you have some extra water content coming in from the syrup.
You do need to be really careful when adding water. It will sputter and spray very hot sugar on your skin. Since it is sticky it is going to stick to your skin and burn. If you get some on you, run it under cool water. It will quickly cool off and you can wipe it off.
No matter how badly you want to mess with it, let it be. You don't need to stir it unless you are adding water. Let the heat spread through the syrup evenly as it boils. This is an early picture about five minutes into the boil.
Although it is fairly boring to watch boil, you do need to keep an eye on it. As it starts to thicken it is going to get hotter at a faster speed and start to darken much quicker. You need to keep it at a steady temperature so it does not burn. Once you burn the sugar you are not going to be able to remove the burnt flavors and smells and it will definitely carry over into your beer.
It's hard to see but in the lower right hand corner of the pot it is starting to darken slightly. It is my experience when you do this on an electric stove the color will start to appear on the outside and work its way in to the middle.
When color starts to appear that is a good time to make your first water addition. Just a small amount. I like to add it to the edges where the coloring is taking place to make sure it is not getting hotter on the sides than in the middle.
Once you start to get some color it's time to think about where this syrup is going. I like to put it in jars. I boil up water in the jar in the microwave so the jar is preheated and ready to accept a boiling syrup. Adding boiling liquids to cold glass will cause it to crack and possibly shatter.
After thirty-five minutes of boiling I ended up with this. It's fairly dark with a very rich caramel flavor. Unfortunately with so little sugar it won't have a large impact on a beer -- even a one gallon batch -- in terms of color but it will produce a hint of a caramel flavor that might be good in a brown ale or even a dubbel.