You can never get enough practice when it comes to Voiceover or acting. Practice reading Voiceover copy or site reading just about anything is always recommended. One of the hardest things to master is all the various textures of emotion required for Voiceover. This is where you're really stepping into acting. It's why so many people will tell you to take an acting class. One of my favorite YouTube channels is called The Actors Academy and they recently had a video that intrigued me called The Cookbook Method of How To Practice Acting.
It's very simple. First, white down on small pieces of paper various common emotions, such as happy, sad, angry, frustrated, mad, lustful, and so on. Put them in a bowl or hat. Next, Take a cookbook, any cookbook, and flip to a recipe page. Pull an emotion out of the hat and read the recipe with that emotion. Pull another emotion and do it again, You are to be recording or filming yourself doing this so you can listen or watch back and evaluate your performance. If you can read a cookbook with emotions, you will be able to more easily read Voiceover text with realistic emotion. I find this to be a unique and refreshing way to practice,
It doesn't even have to be a cookbook. Sometimes I do this with Voiceover copy or even just one line of copy. Say the line in a variety of ways. Remember to be true to the emotion. Don't act like you're frustrated, be frustrated.