Antivirals if needed. Since herpes type 1 virus infections happen to the great majority of the american population, it is extremely hard, if not nearly impossible, to prevent oneself from getting infected during his lifetime. So, if one has cold sores, and just mild ones, 1-3 times a year, no prevention is recommended. For people with widespread or frequent outbreaks, doctors may prescribe daily antiviral medicines.
YES. The most common trigger is UV sun exposure, especially early in summer. Frequent use of a stick sunscreen (SPF 15 or greater) reduces incidence. Any fever or and injury to the face, especially the lips is another trigger. Topical for herpes are not very effective. Acyclovir or valacyclovir pills (I favor the latter) are very effective and very safe. Taken at first symptoms they make it milder. Ta.
Antivirals. Just to add to the discussion, when using antivirals, I usually start with acyclovir. It's reasonably successful and pretty cheap. If that doesn't do the trick (which it usually does), then I go to valacyclovir. It works a bit better, but it's also significantly more expensive. If that doesn't work, there are other things to try, but I start to consider other underlying immune problems.
Lysine. The use of lysine 500 mg per day can reduce your out breaks of cold sores.