i started out my studying other spells, and altering them slightly to be more personalized. you should get a pen and paper, start by figuring out what you want to accomplish. we'll go with luck as an example. next, write down some things associated with luck, could be symbols, colours, items, crystals, or herbs. third, figure out what type of spell you'd like, a candle spell, a honey jar or witches bottle, a potion, a charm.
let's go with a satchel, you took an aloe leaf, a green drawstring bag, some cinnamon incense, and agate. you then choose to pass each item through the smoke and say a chant, say it's something like 'with this (item) turn my luck around, only good fortune shall abound, so mote it be'. write down how the spell went, then carry the satchel for a month, record if your luck changes. if it doesn't, go back to the spell and see what you can alter, or needs fixing.
spell writing is sort of trial and error. start small with things like luck and money, before toying with love spells or curses or things like that. study will help you as well as experience. keep in mind, the chant doesn't have to rhyme if you don't want it do, and you can use as many items as you want, just be sure they all have the same properties as the spell you wish to cast. lastly, some items you'll have a stronger connection with than others, if you don't like one, substitute it for something you do like. hope this helped.