how can you stop getting lens flares in your sun photos?

Use your feet. Move around. Recompose. Either get the flare out of the shot or use it as part of the picture. 

There are a few ways to minimize flare.  The most common thing to use is a lens hood.  The hood places a shadow over the lens thus eliminating flare.  Many lens manufacturers have hoods specifically designed for each lens.  These "tulip" style of lens hoods are the best option and if one is available for your lens, use it instead of a generic rubber, plastic or metal hood.  Older lenses may need generic tube style or collapsible rubber hoods.  Of course, you could use anything such as a card or your hand to cast a shadow over the front element of the lens.

If the bright light source is in the frame, then a lens hood is not going to do anything.  In this situation you can take two shots: one shot with your hand or card over the Sun to eliminate the flare, and one with the light source in the scene.  Then blend the two images in post.

Buying lenses with excellent coatings (e.g. Nikon's new Micro Coating) can greatly reduce flare.   Only buy multi-coated filters such as those by Hoya, Tiffen, B+W and Heliopan.  Remove any non-essential filter(s) to reduce the chances of flare.  The fewer pieces of glass, the lower the chances of flare.

Keep your lenses and filters clean.

If at the end of the day you simply cannot avoid flare, then your only option is to embrace it and try to creatively work it into the shot.

Use of a lens hood.  UV filters will NOT help in reducing flare.

Use a lens hood or shade the lens some other way- filters won't help.  You could try using a very small aperture (f22 ish) and go for a starburst effect.

Try a screw on hood or use a UV-filtering lens filter.