Bottle carbonating beer isn't a complicated process, but to get consistent result across many batches requires a bit of extra planning.
First things first - make sure your beer has completely fermented before bottling. Don't just rely on visual signs like the airlock bubbling, take a hydrometer reading and then take another one to make sure it is stable and not still dropping. When you record you final gravity, you should make sure that your attenuation is as expected. If your attenuation is 65% and the listed range for your yeast is 75-78%, you've got a yeast health problem and may want to repitch with healthier yeast. If you have excellent yeast health to start off with from using a fresh culture and yeast starter it makes getting consistent bottle priming results a lot easier and quicker. For more info on attenuation, check out our article on beer attenuation.
To dial in your priming sugar amount, use our Priming Sugar Calculator. It will ask for the volume and temperature of the beer - why temperature, you ask? It's because the beer retains some co2 from the fermentation. The amount of co2 a liquid can hold is dependent on the temperature of the liquid. The colder it is, the more it holds. The same beer, with the same volume, and the same amount of priming sugar could end up with different carbonation levels if it is brewed and bottled in July instead of December. The volume of the beer is also quite important. It's tough to tell the difference between 4.5 and 5 gallons in the carboy, but that 10% difference will definitely wind up changing the carbonation level with the same amount of sugar. If you haven't already, mark your carboy with some tape at each gallon mark by filling it up 1 gallon at a time. Additionally, for optimal results, weigh your priming sugar instead of measuring it by volume. Our Pocket Scale or Grain Scale are good options for accurate weighing.
They say there are only four ingredients in beer: malt, hops, yeast, and water. And some smartypants try to say that time is the 5th ingredient. But co2, while a "byproduct" of the yeast fermentation, can be treated just like an ingredient - it can dramatically change the flavor and experience of the beer. How much co2 you want in a beer depends on your preference and also on the beer style. British Bitters or Milds are wonderful at very low carbonation; Hefeweizens or Tripels can benefit from high levels of carbonation. Our priming calculator makes some suggestions based on style and beer kit; you can use these as a starting point.
Now that your brain is primed with knowledge, go carbonate yourself some beer!