I think the advice you'd give to new players is the same advice you'd give to any players, and it has to be based on what the current best known strategies are in the game, i.e. what the top players do. The best strategy has changed a few times since the game was released, and I'm sure it will change again.
In no particular order, the main ideas are:
1. Aggressivly push to medium range. Little damage is done at long range, so pushing to medium maximises your damage and also pushes your opponent, especially if you have many pushing at once. This is critical. Don't push when being attacked (I don't always follow this rule)
2. Retreat early when being attacked by units at medium range. Don't wait until your shield is <25%, otherwise those enemy units attacking you at medium range will continue to attack you as you move into long range, which is something you want to avoid with such a low shield. If you're being attacked my a machine gun and shotgun at medium range then you'll probably want to retreat at all shield/health levels.
3. Pay a lot of attention to your opponent's sniper. Your sniper should prioritize attacking the enemies sniper. If your sniper hits the opponent's sniper then it's probably worth changing the attack target of all your nearby units to it even if they are attacking medium range units (and only if it is safe/worthwhile doing so)
4. When attacking, tend to prioritise enemies that are already being attacked by your allies. If no enemies are being attacked by an ally then only attack enemies that are attacking or retreating. If no allies are attacking or retreating, then push(move) towards your enemy.
5. The shotgun should not always start shooting at the first unit it sees at medium range. Its good to get as close as you can to medium range units, especially if they are retreating or being attacked by an ally. This will give your shotgun more medium range shots as the enemy unit tries to escape from medium range. One of my SG rules is that it will only stop moving towards medium range units when at-least 2 units are in medium range.
6. The best way to collect resources depends on your current strategy and how well you are doing against the playerbase. Your resource collecting strategy will change as you change so I can't recommend one specific technique. It's ok to not focus on resource collecting while you hone other more important bits of your AI.
7. Minimise the time you spend switching your attack target. I have rules for when to switch. For the sniper and machine gun, whose reload time is quite long, it's especially important.
8. New players can totally ignore tagging for now when . They will waste a lot of time with them if they start using them.
9. Group your units together. Players do this in various ways. Many will move the unit to the nearest ally during a game if they wander too far away. I don't do that.
The above are not strict rules and there will be many exceptions, but I believe the top 3-4 players apply most of them in some form or other.