Don't become personally attached to fiefs.  Don't look at them as extensions of your personal castle. They're not.  When you adopt this philosophy, you're a lot happier in game.  Fiefs don't give much at all in tribute, they are far more valuable as raids so they will get raided.  Accept that.  Siege another, or resiege that one.  Just don't go to war because someone raided your fief.  

Everyone else has covered the essentials. Focus on player development in the early days and don't do offensive actions and do protect your resources and troops throughout.  

Grind.  Every day.  Keep the sages working round the clock, keep the build ques as full as you can all the time. 

Never react in an emotional state. That's how they beat you. 

LOL "Upgrade your warehouses and barns to the maximum level then tell people how much resources you have"... Is this a guide on how to become a farm?  When I find people who do this I raid them until they quit, that way I can farm their sector for resources at my leisure. 

My best advice:  look where a beacon is before attacking it.  If a beacon is in a top league's area and some small league is holding it, they probably have an agreement with the big league (or just recently took it, and are about to get smashed). If you take the beacon from the small league and try to hold it, the big league is probably going to get mad at you.  And while the response "but we didn't take it from you, we took it from somebody else" may be true, it won't make your troops any less dead...

Why would you raid people until they quit?  The fewer people playing, the less interesting the game.  You max your warehouses and barns to USE those resources to build strong troops and upgrade buildings and lost arts.  You max your resource producers too.