Highlight your skills that you have developed working casual roles such as resiliency, managing expectations, organisational skills, extra curricular activity, confident and outgoing.
I'd recommend that for both the group and individual interviews you try your best to relax and not worry too much about demonstrating technical aptitude. It will probably be a bit different from your experience in university, but I got the impression that the key things that the company was looking for were confidence, self awareness, a structured approach to problem solving, and good interpersonal skills. For the group workshop task, try not to be the person coming up with all the best ideas, instead be the mediator.
BE HONEST. There isn't any point in committing to a position which doesn't fit your needs. Understand your strengths and areas you want to improve prior to interviewing.
Be prepared but also be yourself.
Prepare. Be proud of yourself without being cocky. When asked about weaknesses although mention how you manage them or how you are working on improving them. Don't pigeon hole yourself in one industry as construction works across all industries.