To reduce flare, first shade the front element as much as possible. A lens hood is the main tool for this, but it helps most when the sun is just outside the frame; if the sun is actually in the frame, its benefit is limited.

Also remove unnecessary filters such as UV/protective filters, since extra glass adds more reflective surfaces and can increase flare and ghosting.

Lens choice matters. Better-quality lenses with effective anti-reflection coatings generally flare less and keep better contrast. Multicoated lenses help a lot, and newer coating technologies can improve resistance further, though no lens can completely eliminate flare with a very strong light source like the sun.

In short: use a hood, keep the front element shaded whenever possible, avoid extra filters, and use well-coated lenses if flare resistance is important.