Bike mechanics does require a lot of skills and knowledge; nonetheless, there are few things than can be done easily to take care of your bike properly and a set of tools and spares that you should always carry with you on any ride.
The drivetrain and chain are the dirtiest parts of your bike. Whether you have a mountain bike or a road bike, this dirt can affect longevity and performance or your bicycle. Dirt increase the rate of chain wear, reduce the flexibility of chain links, and impair your shift performance. The derailleur assemblies and drivetrain cogs also get severely distressed. Apply cleaners lubes and on a regular bases. Always wipe the excess lubrication with a clean cloth, as over-doing it might attract new dirt. Every few months you have to completely remove the chain by using a chain-removal tool and perform extensive brushing. Then soak it in a chain solvent to get rid of the build-up filth. You should consider having a compact chain tool or a multi tool that includes one with you at any ride, so that if your chain snaps, you can fix it up well enough to cycle home.
It might seem a trivial thing to do, to keep your tires correctly inflated, but you would be surprised to discover how often novice cyclist simply don't do it right. The first step is to choose the right Bike Pump for your inner tube valves. There are 3 types of valves: Schrader - wider and flat, Presta - long and narrow and Dunlop valve, slightly less common. Then you need to consider where and when you want to use your pump. Standing or Track Pumps are more powerful but they cannot be carried with you, while Mini or Frame pumps will require a bit more pumping action, but are needed when you are out on your wheels. Third step is to know the right pressure for your tires: typically, a road tire stays 80 and 130psi, while a MTB tire holds 30 and 50psi. Hybrids and cyclocross usually take between 50 and 70psi. It is a good idea to have always a spare inner tube with you, or a puncture kit and a mini pump too.
Never tight too much any bolt, not let it be too weak. And never ever risk to wear them down. Use only the right tools for each element you are tightening: allen keys, spanners, and wrenches. Other bike tools, such as cassette tools, or bottom brakets tools belongs to the workshop of the more experience cyclist, who might want to save their backs and add to their maintenance equipment also a workstand. As we talk about tools, it is a very good idea to always carry with you a multi tool. Having the right tools to repair your bike when it goes wrong on the way is essential, and those compact set of keys and spans will make sure you have almost always the right tool at hand. They are very light and can be carried in the pocket of your jersey or in the saddlebag. Last tip: when you are maintaining and fitting your bike you will get dirty, this is mathematic. Make sure to buy also some hand cleanser and hand cream ;)