If you don't have the money to purchase a nice flashlight / laser attachment for your sidearm, this thread may be just up your alley.
These pictures are examples of different stances you can take with your flashlight. There are positives, and negatives with each stance, and each stance can be adapted / manipulated to meet your specific needs.
Picture 1 is my preferred stance when using a flashlight. My reasoning for this is it closely resembles the stance I already use whenever I am engaging one-handed.
Picture 2 is the first variation of holding a flashlight. I call this the "hollywood" stance since it is seen in many action movies and television series out there. some people like this, and prefer it over others. I do not like it because it feels unnatural to me, and there is no benefit to having the flashlight wrapped under my strong wrist (i.e. recoil reduction, easier sight alignment, etc...). Everybody is different, and some people swear by this stance. If you find it works for you, then use it.
Picture 3 is different from the first only by the fact that the flashlight is extended out 100%. Some people prefer this to having the flashlight close in.
Picture 4 is a variation based on the assumption that the assailiant will fire at the light, and by holding the flashlight in this manner you will be changing the assailiants point of aim away from your vital areas. This is a good theory, but in all honesty, I view this as an akward way to close a flashlight in close quarters. I would not dismiss this tactic, as I see where this could be used successfully is space allows.
Practice all of the techniques and see what works for you. I also invite you to get out there and find the local tactical instructors closest to your community, and attend some training classes. Open your mind to as many different techinques as you can, then adapt and choose which ones work the best for you.
Stay safe, secure, and informed.