General


Some general thoughts and observations:
When should you upgrade? Should you upgrade everything? Just your offense? Maybe you've seen advice online that makes it sound like if you do the wrong thing, you'll totally ruin the game for yourself forever. First off, relax. Unless you are a super-competitive player who intends to be at the absolute top of the leaderboard, it'll be okay. And if you are that kind of player, you probably don't need this guide.

There is really only one unrecoverable mistake. Once you increase your war weight (see here) you can never decrease it. The more competitive alliances won't accept you if your war weight is too high. If you plan to war with a competitive alliance, plan carefully. Check their websites for their requirements.

With all that said, the main thing to consider when deciding if it time to upgrade is what kind of player you are. Here are some common situation. You may not fit exactly in one of these buckets, but hopefully this helps:
Regardless of your play style, unless you are certain you want to be uber-competitive, consider upgrading pretty much everything before you advance from Gunpowder Age to Enlightenment Age. All buildings, everything available in the library, the first three university categories - everything except maybe the more expensive wall levels and the slower university categories. It'll take awhile, but it will make future ages go much more smoothly and give you a solid foundation no matter what play style you end up choosing. Oh, and when I say upgrade your "offense", I mean only the stuff worth upgrading. See the Attacking page for some strategies, and which troops get used in them. Ignore the rest. So for example, there's no reason to upgrade a MRL, even once, ever. Don't waste your time on junk. The only risk is that they rebalance the game where the junk troops suddenly become awesome. But that seems unlikely at this stage in the game's lifecycle. And if it does happen, you'll be in the same situation as everyone else.