It would be wise & recommended to start 3 side missions for each primary mission based on majority tips of gamers. Side missions will enable you to step up and gain admittance to better weapons and aptitudes and capacities that will help you in the primary journeys immensely. Additionally side missions are a great deal of fun.
You can begin the side journeys from the earliest starting point since some of them will be bolted off after you achieve a specific stage in the main game story.
There is a primary journey wherein you travel to a place by using a boat to discover ciri and after which all inadequate side missions will be flopped consequently or failed automatically.