First you must have clean hands so:

• Wash your hands with soap and water 
• Use hand sanitizer 
• Use latex gloves

Either or all of those will ensure that you do not get skin oils from your hands on your comics. Then get a bag and board out and ready.

• Place the comic flat on the board
• Guide the board and comic into the bag
• Gentlty slide them
• Tape the bag shut if it doesn't seal on its own. I prefer painter's tape or masking tape for this.

This will prevent any thumb marks you may see on older comics from pushing a comic into a bag with board too hard. Also make sure that you are sitting down and not standing up in case you drop the comic. It is less likely to get damaged in the fall as the distance is shorter.

When storing comics you should have them face each other, especially if you are storing them for a long period of time as this will help prevent spine roll. Then you just use this pattern for storing your comics.