This may not be perfect but it's my first tab so go easy on me.
It's best to keep your 3rd and 4th fingers on the third fret of the B and e strings the whole 
time like you're playing a G chord

                                           G
e------------------------------------------3------3--3--3--3-----------------------
B------3------3----------------------------3------3--3--3--3-----------------------
G----0------0--------0--------0------------0------0--0--0--0-----------------------
D--2------0--------0--------0--------0-----0------0--0--0--0-----------------------
A----------------2--------3--------2-------2------2--2--2--2-----------------------
E--------------------------------3---------3------3--3--3--3-----------------------
                                           D      U  U  D  D                       
                                           o      p  p  o  o                      
                                           w            w  w                        
                                           n            n  n