Some general tips:
- There are a LOT of extra content items (the duplorcator has already been mentioned) that can really add to the game in terms of how easily you can make stuff. The fill can is also a good pick, as it allows you to easily repaint any connected bricks of a certain color.
-Brickpacks are always something to look at. Depending on what you're going for when you're building, brickpacks allow you to easily get or build the shapes that you're looking for to give a build and edge (sometimes literally!) that you might not be able to get quite as easily or effectively with default bricks. Tophius' bricks on RTB are an easily-accessed example.
-Colorsets, like brickpacks, add to what you can build even more easily. Color alone can quite change how a player sees a brick and lets you paint your build with unrivaled detail. A good colorset tends to be varied, full of useful colors, and hopefully soft on the eyes! A good example is Trueno's colorset, also available on RTB.
-Learn and practice! Look around the gallery or good servers, and remember what you like next time you start building. Consider how and why other people use bricks, and if it seems good to you, use it.
-Try out
RTB. RTB is a big ol' system meant to make managing Blockland easier in general. Certain add-ons will have preferences that you can change easily via RTB, and it also allows you to modify certain server settings (entry message, fall damage, certain per-player limits, etc.) while in your server.
-Make things convenient! Certain client mods such as /gethex or the adminball shifting fix, make your life a little easier without changing how your server behaves. If you like how Blockland is without too many add-ons client mods are always still around
-Scour the forums! Some useful information or add-ons are sometimes buried due to how old they are, but many are still useful or relevant today. Other times, they may be in boards you wouldn't expect. Searching before you post is a rule of thumb oft cited but I don't think you'll need to worry about it too much.
I'm not so sure if all of these are such good bits of advice but I find that they've been alright. Good luck!