Once you've completed a mission you can replay it again through the menu. If you mess up at any point then just quit the mission and replay it again.
I did this in Chapter 1 - Danger from above, the first taxi mission with Emile, Anna, Freddie and your dog escaping from Germans on the road from Ypres. Now the first thing to notice, and it's pretty hard to avoid, hazards appear in time with specific notes in the music. This makes the level very fun but also very easy to predict the hazards. So you can play a level a few times and you'll soon learn where and when everything is coming but if you don't want to I've made a short list of the hazards for this mission below. I'd advise pausing between each section if possible to prepare yourself for the next part. Also if you're in a moment of clear fire head to the middle so you have more options available to you.
Random bombs, you have 2 or 3 seconds warning and there are 2 on screen at a time so use this time to dodge out of the way and prepare for the next ones to fall.
Machine gun fire from left to right. Once you see it stick all the way to the right screen and it will disappear before it hits you.
Exactly the same as before except the machine gun fire is from right to left this time.
Fast paced bombing, to begin with it goes in a line from left to right then becomes random.
Blimp appears and begins dropping 2 bombs at a time but they are always far enough away from eachother that you can place yourself between them no problem. He stops after a second then drops 1 more pair quickly so beware when the music slows down.
Mines begin appearing across the road so stick to the following directions after each wave of mines: right, left, dead centre, slightly left.
Exactly the same as section 1 with random bombing and machine gun fire from left to right, followed by 1 quick paced bombs in the far right.
2 random bombs and machine fun fire from far right to centre followed followed by another 2 random bombs and machine gun fire from far left to centre. The music then slows down and picks up again with 3 pairs of fast paced bombs. Careful because this is what killed me the first time around as they're very close together.
It's a dead quick mission and should take you 5 minutes per each attempt if you're reading through this as you go. It took me 2 attempts whilst trying to take notes for this as well and I'm usually bad at these kind of missions.