This thread show you the basic defences which will help you improve your base and make it a safer place.
These are the BASICS, no overpowered defences are on this page. Building 1-3 walls using this guide won't help you, you either need to look up some very good defences (google, other faction servers sites etc.) or make about 40-50 walls.
1. The 'basic' cobblestone wall, cobble stone walls can be easily made with 1 bucket of lava and 1 bucket of water allowing you to generate a pillar of 256 cobblestone at a time. This defence is one of the defences you'll probably see yourself build a lot, even though its basic, tons of people use this to get their wall number up.
2. Basic sand wall, a quite efficient way to protect your base, people will have to hybrid multiple times to get the sand down to the cannon level. unfortunately its quite time consuming as well.
3. Pillars. pillars are used for corner protection for your base aswell as filters at your walls, these filters filter the tnt and sand and makes it harder to hybrid
Another way to filter the tnt from the sand is to make horizontal layers of cobble.
4. Slab defences. Putting slabs at the bottom of your walls is a must have, stacking sand will get harder this way since the raider has to hammer his tnt down to the slabs first (tnt consuming) there are 2 main ways you can protect yourself with slabs:
5. ALLWAYS PROTECT YOUR WALLS WITH WATER
I hope this will help you build your next base, again these are the basics, don't expact your base to be unraidable once you made about 30-40 walls.
To give you some ideas of well protected bases (this might be a little too much for your first well protected base though):