Do note, some people take to grafting quickly and some do not.
And while a pro should get about 95% take on grafts, an amateur will get less, especially for field grafting which is much more difficult as you can not control the field environment as well as in a nursery. With bench grafting your success should be better than with field grafting, since you have more options and control to protect the graft, such as wax to keep the graft from drying out. Your chances of success will be much higher still in either environment if you can get a successful grafter to walk you through the steps in person. A book, online article, or even a "how to" video is just not the same as getting help in person. It is a learned skill and some apprenticeship is idea, if possible. Else, it will be training via trial and error and the school of hard knocks.
The hardest part is getting the cuts right. They have to be perfectly straight. There are grafting tools that you can buy that can help create a good clean cut to further improve the chances of a good join between the scion and the rootstock (these work best with bench grafting, but can be used for small rootstock diameter in the field). I recommend one of these tools if your scion and rootstock are the same diameter (if not, you will have to use grafting knife and practice). The second hardest part is doing the taping so you do not disturb the joined scion and rootstock during taping, while at the same time getting it tight enough to allow a seamless join so a callous will form, but not too tight.
Despite bench grafting being easier and with a higher success rate, field grafting has advantages especially if you are changing over varieties in an existing vineyard. Another advantage is you do not have to spend time or money spraying the rootstock for the 2 to 3 years you let the rootstock develop a good root system (saving money), and for non-irrigated or dry farmed vineyards this then also removes disease stresses that allow a very good root system to develop improving the long term health of the post-grafted vines. And if the graft takes, you should be able to get a small crop off the grafted vines the year after grafting, so little or no time is lost, and maybe even gain some time if bench grafting vines would otherwise struggle in that same environment.