I hope this is helpful to you.
First, you need to read about serial communication between matlab and arduino. You need to establish communication between those two first.
Then take note of the format of the data coming out of your Accelerometer. In my case, I'm working with IMU and my data format is as an example: #YPR = 2.34, 13.23, -2.20
Then, from Matlab, you need to write a script to be able to read this string and identify any floating-point value.
This is what I did in Matlab. YPR = Yaw, Pitch, Roll
data = fscanf(s); %Read Data from Serial
[Y(count),P(count),R(count)] = strread(data, '#YPR = %f,%f,%f');
Then you have to set up the plot and force matlab to update the plot in real time.
%set() is used to set graphic object properties
drawnow; %force matlab to updata plot instantaneously
The link below is a good place for you to get going. But you need to make some modifications to it though.