The upkeep of your bicycle chain is almost a black art, everyone has a better way and many have different opinions on the topic. However you choose to do it I think the one thing we can agree on is when you oil up that chain make sure the chain is clean. This is the most common problem for cyclists. Liquid lubricants penetrate to the inside of the links and are not easily displaced; however they quickly attract dirt. Dryer lubricants, often containing wax or teflon, have poor penetrating qualities unless carried in an evaporating solvent, but stay cleaner in use. The rule for long chain life is never to lubricate a dirty chain, as this washes abrasive particles into the rollers. Chains should be cleaned before lubrication. The chain should be wiped dry after the lubricant has had enough time to penetrate the links. An alternative approach is to change the chain very frequently (but the cost of what they are now, it is not likely that will happen). Do you remember the good old days when they used to have enclosing chain guards, which virtually eliminated chain wear and maintenance? It would also prevent chains from picking up dirt, and to keep the cyclists legs free from grease and dirt. Another thing is to stay away from wearing white or light colored pants or workout pants. In fact do not wear pants you cannot handle getting grease on.
You will also get chain stretch, which becomes an issue with extensive cycling. Chains generally wear through attrition of the bushings (or half-bushings, in the Sedis design) and not by elongation of the side plates. The tension created by pedaling is insufficient to cause the latter. Because an old chain is longer than needed, its links will not precisely fit the spaces between teeth in the drive train, making gear shifts a problem and possibly resulting in a 'skipping' chain that reduces power transfer and makes pedaling very uncomfortable. If the chain has worn beyond this limit, the rear sprockets are also likely to wear, in extreme cases followed by the front chain rings. Replacing worn sprocket cassettes and chain rings after missing the chain replacement window is much more expensive. At that point just look at getting a new bike, however take care of it and it won't happen.