First you need to consider what kind of spell you want to write. Will it be a rain spell, a protection spell, or maybe a healing spell??Once you've gotten down what kind of spell you want to do, consider your intent behind it. Do you want to make it rain because the plants are drying up? Do you know someone who is struggling and needs some protection? Or perhaps you want to help heal someone who is sick? Dig deep and really feel out the reasons behind why you want to do this kind of spell. You should ask yourself - do I really need to cast this spell? Make sure your spell isn't going to harm others. Is it going to take away free will from someone? If your intentions are pure and not out of spite or hate, then you can proceed. The next thing you are going to wanna do is really consider if you want to use tools. If you do, what kinds of tools will you need? Every tool has an energy you can add to a spell, so consider them very carefully. At this time you may also wish to consider the use of herbs or stones as well, as they too are a type of tool. Remember that if you feel you don't need a tool, then don't use one. Once you know what materials you are going to use, if you desire to use any at all, you can move on to a moon phase, or a day of the week, colors, gods and goddesses etc. Or you can choose not to use one at all. Now is the time to also consider, how fast do you want the spell to work, and what exactly you want the outcome to be. Now comes the fun part. You have all the basic criteria down. You can now start working on the actual writing of the spell. Remember that when you write your own spells, you put your own energy into them, and these will work better because of that. (This same technique can also be used for rewriting other spells that you may find). Once you have the spell written you are ready to plan a basic outline for casting. Here's one you can use to help you (this is based on the use of a candle, and remember this is only an outline, that means it's just here to give you a rough idea).
1) Casting the spell on the day and in the moon that is needed?
2) Anointing a candle (of which colour you would have found out in the step above) with oil and herbs (which you also found out in the step above).
3) Then lighting the candle and saying a rhyme, chant or verse to the god or goddess you are calling upon stating exactly what you want the outcome of the spell to be.
4) Putting your hands over the candle (not so you burn yourself) focus your energies into the candle envisioning them as a bright white light which will power the spell.
5) Then you have the choice of blowing the candle out a burying the remaining or letting it burn down completely which will send the spell out into the universe.
6) Finish the spell by saying: With harm to none, So mote it be. (or something along these lines). You should write the whole spell out as above exactly how you plan on casting it, so you have it in front of you and there will be no mistakes when it comes to casting it for real. Don't forget to cast your circle before the spell, or remove it afterwards.Just make sure you are working in a clean area and cleanse the room of negativity beforehand by sprinkling some salt water around and keeping a bowl of salt in the room to absorb negative energies. Smudging is also a good idea! Don't forget most spells unless specified in it will take anything up to 21 days to manifest although most work quickly if the need is great.