First, conceptually understand what an inverse function is, it makes solving it very intuitive. An inverse function is simply a function which has points (y,x) for every point (x,y) of the parent function. So you are essentially taking all points of the parent function and switching the x and y coordinates for each. Those switched coordinates are produced by the "inverse function".
Mathematically then, finding the inverse function is a matter of solving for x and then switching the variable labels. In this case:
y=2x+1 subtract 1 from both sides
y-1=2x divide both sides by 2
(y-1)/2=x now just switch the labels for the variables...
y=(x-1)/2 so
f^-1(x)=(x-1)/2 is the inverse of f(x)=2x+1
