Do not hide them with the background, nor bury them in amongst pictures. Keep the slides simple and concise. Limit the number of ideas or points on each slide. Busy' slides are difficult to read. Keep your sentences brief and concise.
Short phrases are best and are often referred to as 'sound bites'.
Restrict the number of fonts you use. Two is usually enough - one for providing the information, the other for highlighting. The background of the slide must be muted. You do not want it to be more interesting than the content, so don't let it 'take over' the slide. The background should suit the audience and the topic.