Try to test in the morning when you first wake up. If your period is regular, do it at least a week after period is due. I did it the first few days after my period was due, the result (line) was not clear and I did it 3-4 times. Finally got a confirmation using clearblue. After that, you can make a gynae appointment ;)
for best time, usually it's first pee of the day.. test using digital clearblue pregnancy kit about 1 week after you miss your period.. however for myself, I tested the next day after I miss my period as I am always regular, using a normal pregnancy stick during middle of the day..
It depends on which type of test kit you use. Clearblue can use on the day of the expected period. If normal one maybe few days or 1 week later before test.
Usually the advice is to do it at least a week after period is due. This is because HCG levels will be too low for the kit to detect prior to this