PowerPoint is a great tool for conference (large audience) presentations, which is the context for the advice below.

The #1 thing to keep in mind when you create slides (at least for conference sessions), is that they are there to help you remember what you were going to say (the flow and key messages) and for the audience to get a visual reminder of the key points. Slides are not there for the audience to read what you are going to say anyway. If they were, what is the point of you being there? Slides are not holders for complete sentences (unless you are quoting) – use Microsoft Word for that purpose either as a physical handout or as a URL link that you share with the audience. When you dry run your presentation, if you find yourself reading the bullets on your slide, you have missed the point. You have a message to deliver that can be done regardless of your slides – remember that. The focus of your audience should be on you, not the screen.

Based on that premise, I have created a checklist that I go over before I start a new deck and also once I think my slides are ready.

1. Turn AutoFit OFF. I cannot stress this enough.
2. For each slide, explicitly pick a slide layout. In my presentations, I only use one Title Slide, Section Header per demo slide, and for the rest of my slides one of the three: Title and Content, Title Only, Blank. Most people that are newbies to PowerPoint, get whatever default layout the New Slide creates for them and then start deleting and adding placeholders to that. You can do better than that (and you'll be glad you did if you also follow item #11 below).
3. Every slide must have an image.
4. Remove all punctuation (e.g. periods, commas) other than exclamation points and question marks (! ?).
5. Don't use color or other formatting (e.g. italics, bold) for text on the slide.
6. Check your animations. Avoid animations that hide elements that were on the slide (instead use a new slide and transition). Ensure that animations that bring new elements in, bring them into white space instead of over other existing elements. A good test is to print the slide and see that it still makes sense even without the animation.
7. Print the deck in black and white choosing the "6 slides per page" option. Can I still read each slide without losing any information? If the answer is "no", go back and fix the slides so the answer becomes "yes".
8. Don't have more than 3 bullet levels/indents. In other words: you type some text on the slide, hit 'Enter', hit 'Tab', type some more text and repeat at most one final time that sequence. Ideally your outer bullets have only level of sub-bullets (i.e. one level of indentation beneath them).
9. Don't have more than 3-5 outer bullets per slide. Space them evenly horizontally, e.g. with blank lines in between.
10. Don't wrap. For each bullet on all slides check: does the text for that bullet wrap to a second line? If it does, change the wording so it doesn't. Or create a terser bullet and make the original long text a sub-bullet of that one (thus decreasing the font size, but still being consistent) and have no wrapping.
11. Use the same consistent fonts (i.e. Font Face, Font Size etc) throughout the deck for each level of bullet. In other words, don't deviate form the PowerPoint template you chose (or that was chosen for you). Go on each slide and hit 'Reset'. 'Reset' is a button on the 'Home' tab of the ribbon or you can find the 'Reset Slide' menu when you right click on a slide on the left 'Slides' list. If your slides can survive doing that without you "fixing" things after the Reset action, you are golden!
12. For each slide ask yourself: if I had to replace this slide with a single sentence that conveys the key message, what would that sentence be? This exercise leads you to merge slides (where the key message is split) or split a slide into many, if there were too many key messages on the slide in the first place. It can also lead you to redesign a slide so the text on it really is just explanation or evidence for the key message you are trying to convey.
13. Get the length right. Is the length of this deck suitable for the time you have been given to present? If not, cut content! It is far better to deliver less in a relaxed, polished engaging, memorable way than to deliver in great haste more content. As a rule of thumb, multiply 2 minutes by the number of slides you have, add the time you need for each demo and check if that add to more than the time you have allotted. If it does, start cutting content – we've all been there and it has to be done.

As always, rules and guidelines are there to be bent and even broken some times. Start with the above and on a slide-by-slide basis decide which rules you want to bend. That is smarter than throwing all the rules out from the start, right?