If you have been using an oil-based lubricant, consider switching to a wax-based product. The only advantage to an oil-based lubricant is that it needs to be applied less frequently, but in every other way, wax-based is superior. For instance, oil collects trail dust and other things abrasive to the chain, whereas wax sheds abrasives. A recommended wax-based lube is White Lightning.
If you've been using oil-based chain lube, whether you want to switch to wax or not, you should remove the chain and clean it with a solvent to degrease it before adding fresh lubricant. Depending on your typical riding conditions, using a solvent to degrease the chain needs to be done once a year at a minimum.
~~Derailleur Components~~
Lubricate the pivot points using a good petroleum-based lube. I use Tri-Flow. Next, lubricate and adjust the derailleur cables, which might have stretched over the winter. Adjust so that shifting is crisp.
~~Brakes~~
Again, lubricate the cables. Use either petroleum- or wax-based lube depending on how dusty the expected typical riding conditions will be. Adjust the cables, which might also have stretched over the winter.
Check the pads: is there plenty of rubber; do the pads hit the rims evenly? If using fluid-actuated disc brakes, check the brake fluid level in the reservoir.
~~Wheels~~
Spin the wheel slowly checking for true. The wheel should not wobble at all. If it wobbles a little bit and you have the tools and skill, you can make minor adjustments using a spoke wrench. But if there is substantial wobbling, take the wheel to a shop and have a professional true the wheel.
Check tire pressure, which is bound to be low after a winter of storage. Inflate to the manufacturers recommendations that are stamped on the tire.
Now give the bike a once-over. Is the seat adjustment still a good fit? Is there excess play or tightness in the bearings of the wheels, crank, pedals, and headset? Also, for full-suspension bikes, check the suspension joints.
From this once-over, you will be able to determine whether it is time for a major tune-up. This could range from a few adjustments to cleaning and/or replacement of some parts. Opinions differ on how often a major tune-up is needed. It depends on how much you ride, and how much maintenance you perform yourself.
Whether you do the major tune-up yourself or take the bike to a reputable bicycle shop, every now and then the following maintenance is necessary for optimal performance and safety: repacking bearings and adjusting wheel axles, headset, crankset and pedals; replacing cables; truing the wheels; making overall adjustments, such as to the derailleur and brakes.
