我有一个英国朋友她不擅长交朋友我要用英文给她建议

你可以这么说.
When you want to communicate with people and start friendship with them,the first thing you need to look at is your confidence.Most people want to be friends with confident people.Therefore you need to smile to them first when you meet them and try to talk to them.Even though what you said might just be greetings like 'Hello.' Trust me,this will work because after the first time you say to them,they are going to say it back to you next time they see you.By doing this,you then make a good start for your friendship with other people.
The second thing you need to take care is trying to find same or similiar hobbies like what other people may have.When you talk to people,you need to have same topic as theirs.So you need to ask what kind of activities they would like to do after school and try to find something that is similiar to what you do.If there isn't any and you really want to be friend with that person,I would suggest you to develop a new hobby just like his (or hers).
Hope this can help you.