My mini guide: Always remember to try to get headshots (before grenade launcher) and reload when no aliens are on screen. You should have 8 resource points at the end of first day. Buy the Mini-14 weapon and upgrade each of its stats once, then put another upgrade in its power. Do not upgrade the Mini-14 further. Buy the workshop, then the mine and foundry. Buy the grenade launcher, upgrade it to max upgrades. Remember to aim at clusters for max effectiveness. Buy the lumber mill, reinforced barrier, then defense tower. Buy the machine shop and defense barrier. Buy artillery. Buy chemical refinery and flak turret. Buy laboratory. But Rail Gun. Upgrade Rail Gun to full. You should have no problems killing anything after getting the Rail Gun. Buy the rest of the buildings. This should consistently give you good game results.
to abmin-
for the elf protectors, u generally need elemental arrows to kill them, or else they have too much health. plus, any units in close range will get killed, so use wizards (unless u have paladins which can survive for a little bit)