Lemons are typically available all year, however the price and quality tends to be at its best around January and February. This is the time of year where anyone you know who has a Lemon tree starts bringing them by your house until your house is mostly Lemons.
There are a few different variety of Lemons, most notably Lisbon and Eureka. These are the two most common types of Lemons that you can find are not different enough from each other for most grocery stores to label them as different or for us to discuss their differences.
The third most common type is the Meyer Lemon which is substantially different from the other two. Most interestingly it is not even considered to be a proper Lemon, but more a member of the citrus family that is closest to lemons. It differs from standard Lemons in that it is not quite as acidic, with a floral note. Compared to regular lemons, Meyer lemons are thinner- and smoother-skinned, rounder in shape, and have a deeper yellow-orange hue. Though not exactly sweet, Meyers are less acidic than regular lemons, and their zest and juice has herbal, even floral undertones. What makes them interesting is that in cooking you do not have to add as much sweetness to counteract the acidity.
When selecting Lemons of any kind be sure to look fro brightly colored fruit that is free of cuts, bruises, scars, burns, wrinkles, squishes, or anything that makes you cringe slightly. As far as firmness is concerned you are looking for fruit that gives a little bit without being soft, but is also not hard. Basically it should feel juicy inside but not rotten.
The links in the following section will take you to Bed, Bath and Beyond. The items selected are for illustrative purposes, they are not necessarily the recommended tools. Try before you buy.
The most basic of preparations for Lemon juice is to cut it in half and squeeze the juice out. There are plenty of upgrades available for getting the most out of that little lemon and some are listed here in order the most bang for your buck.
For starters, squeeze the lemon over your other clean hand, or a strainer to catch any seeds. Seeds are not very tasty.
Next try rolling the lemon underneath a wide knife, or your hand, or a pan, or a clean shoe, or basically anything that you can slightly crush and roll the lemon without breaking the skin. This breaks up a lot of the "fruit meat" inside of the lemon and gets more juice out of it without any special tools. Another not recommended technique for getting more juice out of the lemon along the lines of the crushing trick is to microwave the lemon for a few seconds. Here are the issues with that; if you cook the lemon too long you are now either waiting for the juice to cool down, burning yourself, or adding hot juice to something which might not react well to that; also it is not nearly as effective as the rolling technique; it makes the lemon harder to cut; and on and on. In short, don't do it.
The next upgrade is to get a lemon reamer or hand held citrus juicer. The reamer is pretty good but adds a lot of pulp. The citrus juicer is in short fantastic and might be the best bang for your buck as far as tools are concerned. The trick is to cut the ends off of the lemon before putting them into the juicer, this allows the juice to pass through the lemon. This tool usually keeps most of the seeds as well.
The next upgrade is getting a non hand held citrus reamer, or an electric citrus juicer. These are the most effective at getting all the juice out of your lemons, however you now have to keep a citrus juicer somewhere in your kitchen. If you are not juicing citrus A LOT, save your money and kitchen space and get a hand held juicer.
There are a few different ways to do this, the best ways unfortunately using more equipment than just a knife. The first way is to carefully cut the zest (skin) off of the lemon and then trimming off the pith (not tasty). This is a great way to work on your knife skills, however it is a pain to say the least. The next method is to use a vegetable peeler to remove the skin in wide "sheets." This works pretty well except that you will still need to remove some pith. The next method is to use a citrus zester, a purpose built tool that removes only the skin of the lemon, leaving behind the pith. This makes thin strips of zest which can be left long or chopped up more finely. The last common method is to use something like a microplane grater, to grate the zest off, leaving behind the pith and removing it in small bits. Once again if you are going to be doing a lot of zesting or have an empty drawer go for the gusto with the microplan grater, if not get the zester. It does a great job, is inexpensive and you can use it to make garnishes and stuff.