How can I give another girl a major oragsim?

It depends on the individual girl. There's no one thing that'll work for everyone, and everyone has their own little foibles. In sex the most important thing is communication. She needs to indicate when you're doing something she likes and you also need to discuss with each other things that you like.

If the person consents that it depends on the person. Without their consent you probably shouldn’t push the topic any further. Some people don’t want this type of interaction and might be startled by certain approaches. If the person consents than just be aware of their comforts and discomforts.