My advice is to meet with your team and take the time to create the theme foundation that can be adapted and reused later, as a template, in different settings or different presentation needs.
Make use of:
Make use of Slide Master to configure the layouts that are used commonly for your clients. PowerPoint comes with pre-designed layouts that you can switch on each slide. But sometimes, these layouts doesn’t fit well in a presentation. Using Slide Master, you can modify the default slides to match your own styles or you can add new slides.
Why bothering adding a new slide via Slide Master? Imagine that you want to make a presentation containing a big text over a solid background as the chapter slide. Then, create a slide with the text centered on the slide, add a text placeholder and choose the default size. Assign a name and then every time you want to use it in the normal presentation, switch the slide layout to use it.
Make sure to use Theme Colors so you can adapt the colors for each particular client. This is a huge time-saving tip if you want to save a lot of time later adapting the theme for a particular client.
Theme Colors have a great benefit vs. the use of Standard Colors palette. It allows you to replace the colors globally for the presentation instead of going over every slide replacing individual colors. Although, do not think Theme Colors are the best choice all the time. Using Standard Colors is also good in some situations (i.e.: imagine that you are creating a Traffic Lights illustration or diagram for your presentation and need to make sure the light colors remain as red, yellow and green, use Standard Colors in this case).
Use Shapes whenever is possible:
Instead of relying on background images, you can use shapes graphics in PowerPoint. Shapes can be edited very easily in PowerPoint to match any presentation requirement. Moreover, combining shapes with Color Themes you can customize the presentation colors very easy.
Shapes are very useful to make diagrams, indeed. You can save slides with different useful diagrams in a presentation bundle (ie: having a different number of steps or design variations) and later reuse them in your presentations. Again, if you spend time configuring your Theme Colors you’d be able to easily adapt the final presentation colors uniformly with a few clicks.
A few other tips while preparing your foundation.
- Use a proper alignment for text. If you are using placeholders in a diagram with different elements, make sure the text paragraphs are aligned properly so when filling the information the layout won’t be broken. This is specially useful for text around circular diagrams.
Use a proper alignment for shapes and objects. Having the shapes selected, you can align all the shape together to the left or right or use the Distribute Horizontally or Vertically options. This aims to have a pixel-perfect presentation.
Get inspired by the job done by others. SlideShare could be a good source for inspiration where you can discover some of the best presentations for any particular category or during a given year. About Graphic design, Dribbble can be another good source to get inspired.
If needed, rely on presentation providers
Ultimately, if you don’t have the skills or knowledge for this kind of job, or just want to rely this on someone else, I’d suggest trying a PowerPoint presentation provider such as SlideModel.com
SlideModel.com is a subscription-based website with different plans available and thousands of PowerPoint graphics that you can reuse. I think it is a good choice if you are looking for a cost-effective solution to get access to presentation templates (indeed, it can be used by design agencies like you or any commercial presentation you need). Designs are advertised as 100% editable and definitely the best thing is that they have a top-notch support (see reviews here).
If you are looking for free graphics, there are plenty of free resources available as well. Here are some of my favorite ones:
http://slidehunter.com - It is a free presentation templates resource with thousands of business slides, business models, backgrounds for presentations and slide designs. There are some good templates available with a relatively high quality. Very useful for business presenters but also for educators & teachers.
http://freegoogleslidestemplates.com - Templates available here can be opened directly in Google Slides, but you can easily export the slides to PowerPoint. I know the creators and they are very friendly and bright people, so feel free to drop them an email if you have any special request.
http://ppttemplate.net - PPT Template includes a collection of presentation template with photo backgrounds and a variety of designs. Designs may not be the best but you can grab some nice abstract backgrounds for your presentations.
http://www.free-power-point-templates.com - Contains a huge collection of presentation designs. It is one of the oldest resources for presentation templates. Includes different categories and designs for different presentation purposes. From education to business, also including free abstract backgrounds and ideas that can be used for inspiration purposes.