Don't spend gems during the tutorial keep'em for later.
Mind your resource before anything else. Build more farms and upgrade your existing farms as high as possible.
It is better to build a concentrated sport for your defense by using available towers, barricades and ultimately your trap on that spot. All the in one spot brings much more damage to your enemies when they attack.
Upgrade your castle gate in order to improve every aspect of your defense.
Don't forget that you can upgrade two buildings at once that also works with troop, defensive building and spell or you can purchase another worker.
You can get free gems in daily quests so keep an eye on those.