1) Try a few takes, but try not to overdo it. In my experience, the first few takes will feel more natural and spontaneous, but if you record the same reference 20- 30 times, it will start to feel repetitive and the acting will not flow.
2) Sometimes I ask friends to do a take or two for me. Sometimes other people can come up with surprising acting ideas for a shot, things I would not think of by myself.
3) The other important thing is to get all the technical stuff out of the way: make sure the camera is well positioned on a solid tripod, the angle is good (similar to the shot), there is enough light, etc. It's hard to get good acting when you have to stop all the time to fix the lights, the camera angle, the tripod, etc. Take enough time to set up well, so later you can forget about it and just focus on the acting.
4) Try to get some acting experience! It can be a lot of fun. Improv is probably a good way to start, but there are many ways to get some acting training, which can help an animator hugely! And it's also fun!