Note the external flash distance with the subject. In general, the flash will work effectively at a distance of 3 to 5 meters. Closer than that subject becomes overexpose alias too bright. Conversely, too far distance tends to produce underexpose or dark images. This can be necessary for the people who really interested to buy Nikon flash.
Make sure the shooting target is within the allowable range if you want to use automatic mode on the external flash. It’s a good idea to read the external flash manually to find out the effective strength of your flash. Each brand and type usually has its own specificity.
Then, use an adequate ISO. This ISO is related to the above two things: the condition of the space and the distance of the shooting. Low ISO is usually used inadequate space such as in meeting room, indoor or outdoor shooting.
We hope this small piece of info can help you to get the better shots from your camera when you use its flash.