Hi Eman
Well done for being invited for an assessment. I know everyone says it, but try to just relax!!!! If you've prepared yourself for all the possible questions then you should be ok.
I had mine a few weeks ago and got an offer of employment 4 days later.
A few tips. On the group assessment, they will probably only be about 4 other people with you. By this time you would have already got to know them while you are in the waiting area. Try to get there a good 40 mins before so you can strike up some rapport witht he others. All my group were fantastic people.
Whatever your group assisgnment is DON'T PANIC!! Even if you feel you haven't got a lot to contribute, just make sure your voice is heard, be part of the team and don't lead. Just make the odd suggestion and acknowledge the other's comments. It really isn't all that bad you know. BE yourself...unless you're gobby!! LOL Only joking.
As for the 2:1 interview again be yourself, check your body language when you are sitting opposite them. Keep hands relaxed on your lap and lean a little forward when answering , keeping eye contact.
If you are stucjk for an answer just ask if you can come back to it. If you really can't answer something, then be honest and say so, don't waffle and go astray of the question. I couldn't answer one question and told them.
Important. Try to remember all the names of the people from your group assessment and also something about them i.e. what they do or where they live.
Lastly, have different examples of answers to your application questions. Examples of difficult times, team work, someone you didn't get on with at work and how you coped with it, why you want the job, why BA, and what you can offer. Take your time with your answers, don't rush, take a few moments and construct your answers in your head before you speak.
The 2 who interviewd me were lovely and very friendly. Don't forget, they want you to do well, there not there to intimidate you.
I hope this helps and I hope you are successful. I'm sure you will. Just give it your best.