influence means to have an effect on the way someone or something develops, behaves or thinks. i don't want to influence your decision so i'll keep my opinion for myself. affect means to cause a change in someone or something, or to change the situation they are in. smoking affects the lungs badly.

INFLUENCE(n) 1. effect on something: the effect of something on a person, thing, or event Picasso's influence on the course of 20th-century art 2. power to sway: the power that somebody has to affect other people's thinking or actions by means of argument, example, or force of personality She came under the influence of one of her teachers. 3. special advantage: the power or authority that comes from wealth, social status, or position 4. somebody who can sway another: somebody or something able to affect the course of events or somebody's thinking or action He's a bad influence on you. AFFECT 1. influence somebody or something: to act upon or have an effect on somebody or something 2. stir somebody's emotions: to move somebody emotionally 3. cause somebody to have disease: to infect or harm somebody or something with disease 4. pretend to be something: to give the appearance or pretense of something 5. adopt something: to adopt a use, style, or manner of doing something 6 act like somebody: to imitate somebody else's style or character 7. come to be or have something: to assume a particular form or state affect a liquid state hope that answers your question

You will find that affect has several other negative meanings: "He seems to be very affected by his loss." "He is affected by Alzheimer's Disease" In the example above "influence" is neutral but it can actually go either way. It can be deemed counter productive or beneficial. However only your own judgement will tell you; depending on the nature of the influence. "He started smoking under the influence of the other members of the band". "The Government agreed to more ambitious goals under the influence of its 'Green' Parliament minority". In other words your opinion will not be influenced by the fact that "influence" is usually positive or usually negative ;-) Arguably though, "influential" has a slightly positive orientation. "Philosophers like Voltaire were influential in the Age of Enlightenment".