What you really want to do in Evony is get as many troops in training as possible and there are a few different methods for doing this. Cottages at level 9 have 4,500 population or at level 10 they have 5,500. You really don't want any more than 6.
Its important if your using Excalibur not to waste it and only have Excalibur on one hero and move him around to train troops, using scouts to move him it should only take a few minutes to get him to all your cities.
If you produce only one resources you can let the stores fill up for this resources then buy the others, then put your troops on training
You can put your idle population on training at the start of the game but you will find as the server goes on you will use up your idle population quicker than it regenerates. When this happens you need to use a different method.
While you can put your idle population on training, what you really want to do is put the whole of your population on training. This way you spend a day putting on troops for about a week if possible. Firstly put you production to 0 for all resources, next adjust your tax rate to 0. Now its possible to use your entire population for training. Make sure you have a lot of resources in every city, now use your entire population to train one type of troop, split production to every barrack. It takes about two hours for your population to return up full, Keep doing them same, when it does, use the whole population in one go. When you have finished putting as many troops on training as you can, you should have enough for a few days, now you can sell all the extra resources you make over the next few days right away, before your stores go full.
Using Archimedes Notes
To explain this method, lets say you have 20 barracks in your city. What you need to do is put on a queue of troops that will take days to make. So lets say you put on 5000 ballista and split them between the 20 barracks, lets say now that takes 48 hours for each barrack. Now you have 48 hours to put a large queue on training in every barrack. About 10 days worth or more. Put the large queue on training in one barrack then use Archimedes notes on that queue. When you idle population fills back up do the next barrack, then the next and so on.. Eventually you can put a large queue on training in every barrack but you have to make sure that the initial queue you put one leaves you enough time to put all the other queues on training for every barrack.