Having played many solo campaigns over the past few years; a few tips for members who haven't got vast experience of the mechanisms of NTW campaigning :
Unless absolutely necessary, don't rush into attacking the opposition early, except in urgent situations.
1. Take time to build up your utilities to generate greater income, & make sure you are exploiting use of the research facilities & colleges, & gentlemen.
2. Get merchant ships out to the nearest trade node.
3. Make sure you invest cash in the cities that will generate the most income first. 10% upgrade in a new town hall that has income of 2,000 will give more than one that has income of 1,000
A strong income stream is vital to success & paying for armies.
4. Where you can defend a bridge/river crossing in a battle, will give a great advantage. It is costly to try to attack over a choke point like this.
5. Try to avoid being caught in areas of attrition in the winter months. If you can rest in a building/mine/town/factory etc., you will avoid the waste of troops.
6. After winning a battle, do not accept the AI offer to finish the action when the enemy is all routing. Use your cavalry to pursue them & wipe out as many of them as possible. Even a tiny remnant can work next bound to raid your utilities & cause you unnecessary expenditure to mend.
7. Remember that spies are vital to giving you eyes into areas that your troops cannot see. They are not just for sabotage & assassination. But, to assassinate an enemy general just prior to a battle can give you a distinct morale advantage on the field.