To be efficient in producing any documents (Google Slide presentation, customer invoice) I’m always trying to check if there is already a nice looking template that I can use. Starting from scratch can sometimes take too much time especially today where there are some many templates already available. Below you will find some link to free document templates.
slidesgo is free Google Slides and PowerPoint templates library with free use for both personal and commercial projects.
Usefyi offers some free templates in different formats (Word, Google Excel, …)
Selfone and Glide offers 1 PowerPoint template with beautiful mobile devices images.