I second Jenny's post.
I've never done a friendship spell. But I do have some ideas you can incorporate for your spellwork. I don't know whether you work with animal parts or not but for the sake of this spell I will include it. So a butterfly is a great tool for this spell because they are considered social 'animals' and they interact with one another. But I don't recommend going outdoors and find a butterfly to kill. Find one that died naturally. I was fortunate enough to find one in my yard. It died from a natural cause. So I gently picked up the dead butterfly and stored it away in a jar. If you can't find a butterfly then that's okay. You can use other ingredients for this spell.
Now herbs are easily obtainable. You can use herbs that correspond to communication, attraction, friendship and happiness. But you do need to state your intentions whenever using herbs. I would usually hold an herb and state my intention. The herbs for this spell would include a yellow or pink carnation for friendship; allspice for communication and social gathering, it also stimulates friendly interaction and conversation; catnip for happiness and for attraction; cinnamon for amplifying the effects of the aforementioned herbs. You can also add sugar for sweetness. If you're looking for male friends then add a galangan root or moss. For female use mugwort or daisy.
You can combine all the herbs an make a mojo bag. Use an orange pouch or drawstring bag. Add a crystal: a carnelian crystal or carnelian orgonite. You can include a petition. And have a yellow or orange candle burning while putting everything together. When finished charge it on a full moon. Carry it with you at all times.