If your dominant frequency is near zero, you have a constant bias in your data. Try to high-pass filter it with a very low cut-off frequency such that the data is equally distributed around 0. In other words, the mean should be near zero, or you will always see the dominant frequency to be near zero Hz.

If you also want to reduce noise, use a bandpass filter, again with a very low lower frequency. MEMS accelerometer already come with internal filters to avoid artefacts at half of the sampling frequency, but they still produce quite some noise even though the signal is oversampled internally.