I like to think of resistors like gravel roads that you have to drive through
in order to get where you're going. After all, you have to use a lot of energy
to drive along a rough road, and the more rough road there is in your path,
the harder it is to get through it. It really gets bad when there's a lot of traffic
trying to get through the same stretch of rough road.
When you connect several resistors in series, it's just like putting MORE
rough road into the route. It gets harder to make it through the rough
parts, it takes more energy to accomplish it, and the overall resistance
to traffic increases.
When you connect several resistors in parallel, it's just like putting more
lanes of gravel around the part that's already rough. It's still hard to get
through the rough section, but there are more lanes, so more traffic can
get through. The overall resistance (to heavy traffic) DEcreases.