There is a simple method of measuring ketosis and it is called Keto Sticks. These are thin test strips that you can buy at most if not all pharmacies. You simply urinate on the test strip and it will tell you if you are in ketosis or not.
Any shade of purple indicates that you are in ketosis.
To get to this level though you need to make sure you are limiting your net carb intake to 20 gms per day to start. To determine this take the total number of carbohydrates you consume and subtract the number of fiber grams that are in those consumed carbs. This is your net carb intake.
Another way to look at your carb intake is by macronutrient ratios. If you can stay under 10% of your calories coming from carbohydrates then for most people ketosis will be reached.
This means that most of your food intake is going to come from fats and protein. This isn't a high protein diet though. Only about 20-30% of your caloric intake will be from protein. The remaining calories comes from fat and will equal 60-70% of your calories.
Every meal doesn't need to be in this ratio though.
As long as at the end of the day your macronutrient ratios fall into this range you are in good shape. Though the keto strips will tell you without a doubt if you are in ketosis or not. If at 10% carb intake you are still not in ketosis then try 5% and see if that ratio works to get you in ketosis.