Make a documentation when building the website and keep a track record of your changes
The eagerness of getting things done as fast as possible in a first place can result in a future nightmare. Even if you are the only person handling the maintenance of a website it's very easy to forget what you have done in a first place. If you in addition need to let somebody else handle the maintenance, the task for that person might become almost impossible, espacially if the project is big.
There are many different ways to make a documantation and those can be very extensive but I would like to focus only on the a few simple aspects that might make the maintenance of the website easier.
First of all decide on what format you would like to use for your documentation. Some people prefer to write down everything in a Word document. Personally I like to use a spreadsheet program like Excel for my documentation. As an example what I try to keep the track of is the use of external codes (e.g. java scripts) with a short explanation why they are there. Some of the codes are placed on a certain page only temporarly. An example of such a code is 'Falling snow' script added to a site during a Winter season that for obvious reasons shouldn't be there in the Summer. It's difficult to say what you might need to document, as it depends on the content of your website but one criteria I use to define that is what elements of my content will need more or less regular changes.
Name the objects in your project
If you have only few objects on your website it's easy to find them. As the project is growing you add new objects all the time, sometimes create permanent groups etc and in the end you have a list containing a considerable amount of objects called obj218 or obj2112. Even if you created it the task of finding the element you want to change can be very tedious. Giving the objects meaningful names might feel like something slowing you down but in the long run it's actually going to speed you up.