When in doubt, replace the line

Throw ropes get a fair amount of abuse. Most climbers would cringe at how we treat our ropes. Ropes worst enemy is dirt and grit, very common on river banks. Dirt and grit get in between the rope fibers and break them down prematurely. The best way to prevent this is to hand wash or machine wash (daisy chain first). After washing, hang and air dry (don't use a dryer as the heat may damage the rope, especially Polypropylene). At the end of each season, manually inspect the whole length of rope. Pay close attention to any sheath abrasion. If the rope core is bulging out, it is time to retire the rope and perhaps use it for hanging clothes. Here is a great article on rope care from Sterling Rope: Rope Care & Retirement. Here is another good article: REI Rope Care Article.

Avoid sun exposure, keep clean, avoid stepping on the line, avoid sharp or rough edges

All synthetic materials break down with sun exposure as many old-timers know all too well when we used to paddle fiberglass boats. Many inexperienced rope handlers step on ropes. Do this around rock climbers and you will get more than a big frown. Shoe tread collects small particles of silt and tiny rock shards. Both of these get worked into the center of your rope and work over time to tear and wear down the long rope fibers. Another hazard in rescue work is lowering or bending rope over a ledge. Think about how you cut rope, you move the rope back and forth over a sharp surface. Essentially, you are doing the same when you run a line over a ledge. Rock climbers place padding (or run through a large diameter hose) between the rock and rope for protection.

When you first purchase a rope, re-tie the end knots so they are too small for your hand to pass through. Unpack the entire rope and re-stuff. Toss it a few times to get used to throwing and stuffing the rope.