Hey Bichon! The biggest thing with holding the instrument is that you have to have a good shoulder rest setup to keep it level. If you do this properly, you will relieve tension against your neck. Think about how you would sit naturally in a chair–that is how relaxed you want your neck to be. To be able to achieve this you have to adjust your shoulder rest in a certain way, or consider trying out other ones. Once you find the proper height shoulder rest and how it feels, you will be able to get to that natural state.
Make sure your instrument is always level when you play, which can be accomplished by either standing up or sitting. Make sure you sit at the edge or your chair, as this promotes good posture.
I would recommend checking out some of the options I have on my website. The suretone shoulder rest is a very unique option that works for a lot of people. It is highly adjustable and easy to use. It won’t fall off your instrument which is nice.