As many will know, I am an avid DIYer, and tend to work by the principle of 'if you want a job doing properly, do it yourself'. I encourage anyone to have a go at self maintenance. There is usually nothing major that can go massively wrong or that can't be fixed - all part of the learning curve.
The only caveat I would put on is with brakes. Unless you are 100% confident in what you are doing, I would suggest leaving it to someone who knows what they are doing. If something goes wrong with brakes, the results can be absolutely devastating for the driver or third parties. There are also potential insurance issues as it could be claimed that your actions have made your vehicle unroadworthy which would invalidate the insurance.