First of all, you will need the fabric of choice before you begin. I chose two fabrics; navy pinstripe and black leather. 
First you will have to cut your fabric into 10 different pieces;  

2 x neck pieces (black leather)
4 x left and right front pieces (2 x black leather and 2 x pinstripe)
2 x back pieces (1 x pinstripe and 1 x black leather)
2 x pockets (black leather)

It's important that you know your size and measurements before cutting the fabric into these 10 different pieces. 
I chose to have leather details around the neck and pockets, and also the inside of the vest is all leather, which is why I chose to have 2 back pieces. 
The pinstripe fabric is very light; therefore I added the leather for more structure. 

After cutting the pieces I started pinning the neck pieces with the back pieces and sewed them together. 
Although I did not sew all the way around, I left room for the front pieces to attach with the back and neck pieces. 
I then sewed the neck pieces with the front pieces first, and then afterwards sewed the sides of the front pieces with the back pieces.
 As you can see on the pictures I added silver ribbon all around the vest, which I sewed at the very last. 
I then added leather pockets to finish the look.
 And then you have your vest!