The basics of spell casting all boils down to this one simple concept: Spells are directed by the thoughts you envision while casting them. That being said, it is important to be focused while you are casting a spell. Visualize every aspect of your spell's effect. The simplest spell I can give you is to imagine what you want to take place, then write it down on a piece of paper. Just knowing what you want makes it that much more powerful. When you go to the step of writing it down and describing it, something will happen. However, with this being a very simple way to cast spells, it may not turn out exactly how you expected. That is, unfortunately, the nature of spells. There is a lot of "if" involved, and almost always unexpected effects. However, those effects may be livable or even ideal if you cast the spell properly.
If you would like to become more elaborate with spells, there are some things you can do to make them much more potent. Adding corresponding herbs, for example, can strengthen your spell. Herbs have powerful energetic and metaphysical properties. Refer to this site's herb dictionary to learn about the magickal properties of herbs.
Another important thing to consider when spell casting is timing. Consider the moon phase, time of day, and time of year. Waxing moon, full moon, morning, spring, and summer are all associated with growth, development, and manifesting what you want. You may use these times to cast spells to attract new friends or money. Waning moon, evening, afternoon, and fall are associated with banishing and getting rid of the things you don't need. You may use this time to break off unhelpful relationships or to stave off negative emotions like jealously or insecurities.
Seasons and Elements
Consider the Wheel of the Year or the elements when working with spells. Spring symbolizes the element Air, which has to do with wisdom, wit, creativity, and knowledge. Summer is to the element Fire, which has to do with passion, excitement, sexuality, and warmth. Fall is to the element Water, which has to do with peace, love, emotion, and sympathy, and Winter has to do with the element Earth, which has to do with stability, trustworthiness, hard work, and perseverance
The elements also have corresponding colors: Yellow represents Air, red represents Fire, Blue represents Water, and green represents Earth. Use these colors when you want to cast a spell that corresponds to a specific element. Other colors also have special magickal and metaphysical properties. This site also has a guide to understanding colors and their meanings.
The Spoken Word
Readings are often times included in spells. This is because the spoken word is powerful. While thinking is powerful as well, speaking your thoughts and goals makes you even stronger. That is why some witches write rhymes for spells. Not all spells have to rhyme, but it sure makes them catchy.
Another thing you will see witches frequently do is candle magick. Witches sometimes "dress" candles or burn candles with corresponding colors to their spell. Dressing a candle involves anointing it with scented oil or just plain olive oil to conduct spiritual energy and sprinkling certain herbs in it. Sometimes you may even see a with carve a sigil into a candle.
A sigil is a picture or symbol that is drawn to represent something desired. Many people create their own sigils, but you can also use one someone else has designed. To create a sigil, simply envision what you want and use shapes, letters, or designs that remind you of it.
One of the last things I am going to talk about is crystals. Crystals also direct and conduct magickal energy. Common ones used in witchcraft are clear quartz, amethyst, and rose quartz. Setting up a crystal grid around something you want to enchant infused it with magical powers. Imagine the line of energy and power bouncing around all the crystals you have set up, reflecting off each other, through each other, and strengthening the power of your spell. Clear quartz is known the amplify the power of any other stone. For example, if you wanted to enchant a penny for a money spell, you might want to use a crystal grid of bloodstone, clear quartz, and (if you're lucky) a gold nugget. It is important to keep your crystals charged. After using them for a bit, they will get tired. You can charge them in sunlight, moonlight, or even in salt water or alongside some herbs that correspond to them. Just make sure what you do doesn't damage the crystal. Some may fade in sunlight or dissolve in water. Be careful!
This article barely scratches the surface of witchcraft, but I hope it peaks your curiosity and gives you some useful tips. Remember not all witches practice or work with every single thing I listed here. Some may practice with even more things and use different methods. That's okay too. The idea behind it all is to create what you want through thought. Best of luck!