It depends on a whole lot of different things, the experience of the jockey, experience of jockey on a particular track, whether they ride the horse in its work or have ridden it on race day before, environmental conditions on the day.
For me i always try to get the same jockey to ride the same horse so they get to know eachother. If that isnt an option, if I have engaged an experienced jockey I try to let them know anything relevant about the horse, eg in track work it loves to have its head in front or its really lazy if allowed to be, I have to trust that they know what they are doing and will try their hardest. An inexperienced jockey will get more specific instructions. But at the end of the day sometimes people and horses have a bad day and no matter how good a job has been done leading up to the race it goes to custard when the gates open!