So, with this in mind you should treat it as a learning experience. Find your weakness and you will become a stronger Rust player. It's all part of the game. Here are my top 10 common mistakes to check for - this is by no means a full list, there are many other potential exploits. If you know any let me know!
I can't resist mentioning that the Diamond features 'Auto Doors' and 'One-Click Upgrade/Repair' can insure against some of these hazards.
This is by far the most common error. Twig is destructible at all times. A twig doorframe is a classic entry point, or a neglected twig roof panel that can be easily spotted by passing minis.
Don't place windows unless you have a good reason. This is a common noob mistake - in Rust you don't need windows for daylight. Players can destroy (or reach) any visible boxes from outside your base, or even auth on your TC if it's too close to a window!
Also don't use Windows™ - Linux is better :)
This one seems obvious but you'd be surprised how often this happens. Don't leave your doors open. Open trapdoor on the roof is a typical mistake because it's easy to forget and easy to spot from above.
Don't forget to place locks on your doors. I recently fell foul of this myself 3 wipes in a row on my garage door, after 5k hours! It can happen to anyone.
A player can aggro the heli to fire at your base. It's not easy but it's possible, and more likely to happen when you have ongoing beef with other players. The remedy for this is a) don't antagonise people or b) upgrade to HQM.
We run the Anti Code Raid plugin so this is extremely unlikely, but nevertheless don't have a stupid code.
Another common noob mistake. Your base needs a Tool Cupboard with resources in it to keep your base healthy otherwise it will decay. Your TC covers all building blocks connected to it. If you have a separate building it needs its own TC.
Don't sleep too close to the wall. Your foot can sometimes stick out and give players access to your inventory.
The Legacy Shelter does not last long, just a few hours. It's best to log off in a proper base.
Last but not least, be careful who you trust in Rust! Every teammate has the potential to fuck you over no matter how friendly they seem, either deliberately or accidentally. See above for examples of how idiots can make a mess of your wipe.