Very good. I would like to add a few more.
Similar to the “don’t try and do too much” advice (very good advice at that), is not to spread your self out too thin. You can not possibly protect all of your territories, otherwise your opponent will pick your scattered forces off one at a time. You have to know when to conceed territries temporarily and not to leave yourself vulnerable protecting every inconsequential territory and therefor leaving yourself thin and vulnerable. You must stay focused and not get distracted.
Always, always remember -it is far more desireable to do fewer things very well than to do many things half hearted.
You do not just want to win every battle you engage in, you want to dominate every battle. The fewer rounds it takes you to kill your opponent, the fewer rounds he will get to defend, hence the less casulties you will suffer. I am VERY stingy with my pieces -I avoid suffering casulties by engaging in battles where I only have a slight advantage if at all possible -especially more the valuable ones such as fighters.
Do not leave valued pieces, such as fighters unprotected. In a heated war it is very difficult to replace the more expensive pieces, so you REALLY want to avoid leaving them vulnerable or else you are going to lose them and will probably not be able to replace them any time soon.
Also, treat your team like a single country working towards a single goal rather than as separate countries all doing their own thing. Your strategies should be coordinated and you must work together.