We have set our VPS Machines up in such a way that the default settings work great for most users. When installing the client software you install using all the default settings as these will guarantee that you be able to connect to your VPS with minimal of issues.
However you can change a few settings to maximize performance.
Under the connections option you can use the quality slider and set it to maximum. This ensures that you will allocate the maximum amount of bandwidth to NoMachine so you VPS session remain without delay. In addition you can also set the resolution. Be advise to set this to a setting that you are comfortable with and not just set it to the maximum resolution as the higher the resolution the lesser the performance.