ALWAYS be upgrading only buildings required for the next upgrade or two. Do not upgrade anything else, unless you can do so very quickly due to alliance help or builders hut upgrade etc. A quick trick is if you have enough building build time decrease you can just upgrade things
My Strat Especially for F2P players, Aim to upgrade only 1 squad, At the beginning try to maintain a full tank only squad, you can tell its a tank as it has a small icon of a tank. Put a tank or two with shield at the front, then the
Arms race is a permanent event under events in the top right. This is an ever-changing event, it changes its goal every 4 hours, this can be checked by clicking on the calendar. There are 5 different themes 1. Hero Advancement 2. Unit Progression 3. Tech research 4. Base Building