As I’ll probably get my cable on before managing to play with 56k 
I was thinking to spend the next couple of days training my mortar aim. and dinamyte placement.
What are the spots that would be useful to hit from the first try and where from?
for example:
M1- Tank before bridge passing in fuel dump. (trying to target the bridge building site too.
D1- Oasis dinamyte placing from outside the building.
I think immediatly raining mortars on the area where the tank starts in goldrush could be very good for the allies. Get the axis engies as they set up mines, as well as general disruption. You should be able to do this from allied spawn. Don’t do it for too long, or you will TK your engies as the go to repair the tank.
Hitting the various top areas of battery from near the second allied spawn, but out of view of any of the bunkers.
Personally, play axis hard for a couple of days and really watch where people congregate, stand, hide, stage, etc - those are your targets
Ifurita’s right. Mortaring constuctables and stuff is not the best. Only engineers would go there, and only for a quick amount of time. They would never hang around those spots as they’re too exposed. The best placed to mortar are where people hide to get away from regular fire. They tend to cluster together and make easy targets. Also, if a cov ops can spot for you you can get to know where the enemy is grouping together.
A covert ops/mortar combo is nice. The covert ops can relay enemy positions to come up on the mortar persons map.
VERY useful at the beginning of fueldump where a covert can sniper from the hill and the mortar can see when engineers are at the bridge construction site and mortar it while the sniper is trying to snipe them.
Any kind of MG nest can be good to mortar. Not only can you kill the guy using it, but you damage the gun itself. I think the most important MG in the whole game is the Allies’ nest overlooking the train switch on Railgun. Put some shells into that (and also the switch area itself) before your team tries to drive the tug through.
The commandmap can sometime tell you if an MG gun is broken or not. Look for a satchel icon on undamaged, enemy guns.
The other good place to mortar is the Axis ridgeline on Battery. You should generally be mortaring their hilltop and trench- until the assault ramp gets built. Then focus on the top of the ramp, to killl Axis coverts wanting to satchel it. (You can see blue icons on the command map, so you know when to stop to let a friend climb up) I find it easier to mortar the ridge from a higher altitude instead of way down on the beach (but then, I’m not a good mortarist). Also, being higher will let you get a little more ammo from the commandpost.
Gold Rush
Allies: The tank area until you can see your teammates are holding the area and moving the tank. Afterwards the courtyard will usually yield a few kills
Axis: Allied health and ammo depository. After it’s stolen, mortaring the tank in front of either tank barrier is always a good idea.
Battery
Allies: Should be obvious where to mortar. Right above the ramp, near the entrance to the flag, and along that entire ridge and trench.
Axis: First allied spawn point (it’s not spawn camping because they are allowed to change their spawn), the ramp, maybe occassionally the back if you feel like surprising some people.
Oasis
Allies: Health and ammo storage before the flag is captured, upper wall where axis throw down airstrikes afterwards. Axis spawn area and the entrance areas to both guns (clearly defined as the dynamite symbols on the map, so these are easy to know if you are hitting)
Axis: Health and ammo storage after flag is captured, or front of wall before it’s destroyed.
Rail Gun
Allies: If you don’t mind spawn camping, raining unholy fire on the axis spawn is pretty much always effective on maps with more than 10 people. Otherwise, just keep trying to hit the tug as long as it’s not your team riding in it.
Axis: The track switch area is a good place to hit, you can sometimes clear the path of defenders before your team shows up, or knock someone off that MG42 over there.
Fuel Dump
Allies: Before tank is through tunnel, the Axis constructable MG42 and surrounding area is good, or right in front of the tunnel entrance and a little towards the allied side. People love to hide there while they charge airstrikes and the like. After the tunnel entrance is destroyed, mortaring the inside of the axis base is your best bet.
Axis: Tank, tank, tank! Tunnel exits, ammo and health deposits are also good targets.
Radar (This one I rarely ever mortar on, especially as allies)
Allies: The overpass bridge by the main entrance, either two of the radars as long as they are clear of teammates, and the sides of the main entrance are good spots to hit.
Axis: Hitting the truck area will yield pretty good results.
Hope that helps. Mortaring is a lot of fun and can be really effective on almost any map. Especially if you have a covert ops to help you out.