Do you remember when Call of Duty campaigns, or just shooter games in general, were hard, tough and a challenge on the highest difficulty?
Do you remember infinite enemy spawns, them having crates of grenades and spamming them, terrible checkpoints, perfect aim, horrible AI on your team and trial and error when completing it on Veteran?
Well you're lucky, Call of Duty Ghosts is by FAR the easiet CoD campaign to date. I started on Veteran and completed it in 1 sitting within 7 hours, and could've been quicker. Even if you never played CoD before, or are new to shooter games, this is cake.
The AI on your team actually works, they push a lot and have good aim, 9/10 times you're in a squad and one of your fellow Ghosts has a sniper and will constanly pop off the enemy. :)
Aslong as you stay back, use cover, don't try to rambo it out, use the old but useful LT to auto-aim on enemies, you will rip trough this. I died 3 times, all on the last train mission 'cause I wanted to rush it.
There really isn't much to say for this Veteran Achievement, you have a lot of checkpoints quickly after eachother, the enemy AI is weak and yeah, you shouldn't have much problems completing this.
For the space and sea missions, remember that LB is for descending (going down) and RB for ascending (going up). Stay behind cover and pop them off,
Also, if you have any troubles on the Clockwork mission when shooting on the ice in a truck. Remember to shoot the ice INFRONT of the enemies so they will sink in, not ON the enemies as you will mostly miss your shots and there's an achievement linked to dropping 8 vehicles in ice holes :)
Happy hunting, if you have any questions, leave a comment and I will improve my solution. :)