This forum is about growing herbs. Are you talking about growing herbs together or using them medicinally? If the latter I suggest you post your question on the Herbalism Forum and perhaps refine it somewhat. It is a vast and very general request.

I'm going to assume that you mean growing. Some herbs just grow too big too fast and so need their own area/pot. You also need to take into consideration their water needs: some herbs like lots of water and others would rot and so need a drier area. Hope this helps!

Growing highly toxic medicinal ones with anything else that it might be confused with or harvested mistakenly with it is not advised.

herbs like all plants benefit from certain climates or soil or presence of other herbs and plants, if a plant requires much nitrogen it might for example love to grow near a black locust tree, or growing herbs like ramson would be ideal in a wet dark forest environment, so some plants do match together well ^^ everything is connected in nature, and all plants fulfill a purpose for the whole