Rituals are the counterpart of spells when it comes to spell craft. While spells are for a single set purpose, rituals are often times containing multiple purposes or a single more broad purpose. Spells are cast, and rituals are performed. Not only this but spells can be cast by anybody and with a hint of knowing the basics they will work, but rituals take a deeper understanding and touch base with the inner mindset, rituals are complex magic as the forces that go into them are not typically just energy.
When beginning a ritual one should prepare with certain steps. These steps differ greatly between rituals and the very first step is all from intentions. The purpose of the ritual determines the rest of the ritual, and each of the following steps helps determine what follows from then on. Rituals are on the greater side of magic, being their usage is for the deeper focus, such as ceremonial blessings. Rituals are normally containing multiple variables that partake in their quality that besides intent, include tools, symbolism, traditional acts, presentation, time/date, and astrological conditions. Of course not every ritual must cover each of what was just listed to be a generally good ritual, but a sure thing required is deep thought, and strong pre-meditation.
Building the foundation of a basic ritual begins with intent.
Decide on what the ritual will be targeting, and what the ritual is for.
Common ones are certain occasions like the 8 Sabbats, and of course group related activities like the promotion of a member in a coven.
Rituals don't have to have a specific reason for performing them, one can simply have a broad purpose like annual rites merely calling forth a blessing.
Say I wish to design a ritual for asking for a blessing from the elements.
Now the deep thought comes into play...
If you want a blessing from the elements you'll have to design a ritual corresponding with them in some way while conjuring them, or in this case calling them.
To properly design a ritual for your selected purpose you need to think about the tools, concepts, deities, elements, etc... that you'll be using or conjuring.