Now in order to be more like Sammy Davis Jr, you are going to have to do a lot of research. You are going to have to watch just about every video that is available of him, and you are going to have to hear every song that he has ever sung. This way, you will be able to better relate to him and understand exactly where he is coming from.
At the same time, you will learn all the expressions and emotions that he used to put into his craft, which is going to be essential to differentiate you from the weaker performers.
The next thing that you need to do is to go on and dress up like him. You are going to have to use all the references that you can get to get some clothes tailor made to the way he got his clothes made.
This is going to prove to be a little tricky, since you are going to have to learn for yourself how he dressed up, and then try and communicate this to the tailor who is going to be stitching your clothes for you.
Once the clothes are made, you need to shape for hair and facial hair like him as well. This might be the easiest thing to do, since just about any barber will be able to help you out here.
The last thing you need to do, is to perfect your accent and try and mimic the one that he used to create. This will take some time, so practice and rehearse this as much as you can, so you don't mess up in public.