I have applied online, passed online test (English checking) + answered some questions. In two weeks I have received an invitation for the assessment day. During the assessment day you participate in a different group and individual tasks (the whole process is very fun and interesting).
The assessment starts (actually) as soon as you enter a room! So be friendly, talkative, smile, be nice and dress well! That's what easyJet is about! Tasks were like: build ski jump in a group, speak about the values of the company, discuss how cabin crew influence company (during boarding,flight..) Final task was to discuss some charts and survey and choose the best option. I think they like people who have leadership skills, and who are not shy! Remember to adress people by name!
After you will be called for an individual interview! It is not stressful at all! Girls were very friendly and they really want to see your personality! So smile, be funny and speak about real facts, examples from your life! I felt it was more like a conversation with friends!
My advice: read everything about the company and learn it! You should know CEO name, planes they use, name of founder etc.