Before big presentations, a great way to build confidence and practice lines is rehearsing several times. It may be time consuming and tedious but it is a great way to build confidence, smooth out any imperfections in your presentation and find mistakes.
Try and stand alone in a room which is/is similar to the room in which you will present your PowerPoint. This helps you to get comfortable standing and talking for the given time period.
Think of everything that will be said during and between each slide and take notes of gaps and how to create uniform changeovers. This will ensure you do not get distracted with unnecessary information during your presentation.
Record yourself speaking. This may sound awkward at first but it is a great way to find mistakes and rephrase your speech. Plus it helps to identify your tone of voice and you can make changes accordingly.
Stand in a room with 3-4 co-workers who are familiar and unfamiliar with your presentation. Ask them separately to identify and provide solutions for problems that stand out, give feedback on certain aspects like your delivery, concentration, flow, objective etc. Ask them to also question you on the objectives.
To really know what the audience will be experiencing, you can record the second rehearsal and focus on bettering your stance, tone, voice etc.