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@bunify - indeed, this can be an issue when starting out.  It probably depends (to some extent) on the learning materials you are using - many of those with a more rigorous approach will probably guide you through how, where and when to alter bow distribution, bow speed and bow direction change.  However I'm not a "violinist" - I'm a fiddler - so I won't recommend any treatise in particular - there are others more able to do so!  However - what I found really useful was to take scores that were clearly marked with bow direction changes, and work, almost bar by bar, to fit in to the intended direction-changes indicated.  Doing that showed me - just by practise and trial and error - where I need to speed up the bow, or slow it down (possibly adjusting weight and pressure if required) to fit in to the intended bowing pattern. 

Some of Pierre's beginner pieces are very well marked in this regard - for instance the simple version of Amazing Grace - to be found here - https://fiddlerman.com/wp-cont.....Simple.pdf - not only with direction change, but also clearly indicating slurred runs of notes...    That sort of thing may help, and eventually, you'll just do it almost automatically, even with a score which  doesn't have these helpful indications.