Make sure to research what you want to do in the internet
The internet and several different resources have large amounts of information that have been stored up over the years, websites like Howto are a great source of information with years and years of advice and information built up. Many of these websites often have entire guides dedicated to the specific renovation you want to do, for example many of these sites will have a guide dedicated to adding a better toilet or renovating the garden. Look for these sorts of websites for information.
Before starting the project make sure that your local area is okay with it
Many cities will want to have an idea of where the project is being done and what sort of renovations are being made, large projects will often require usage of land and possibly a permit and inspections. You should also have an expert check out the project and make sure that it is good to go, homeowners are usually allowed to do anything as long as it doesn’t interfere with the functionality of the city, for example connecting illicit power lines to a power station.
Make sure to plan out your project by drawing it on scaled paper
Drawing out your project on ¼ in paper will help immensely with the design process and helps make the construction of the project far far easier. If you are planning a large-scale project often times a blueprint is required for a permit to be issued by the local city authorities many times. Try drawing a profile view, a RTS view and a frontal view. Use a scale and draw with pencil first before committing with a pen. Be sure to read delicious for more tips on this!