Windows Movie Maker 2012 editing

Place the playback marker where you want to make a split. Make splits between each desired portion and the undesired portion. Use the 'Split' function on the Video Tools | Edit tab (or just press 'M' on the keyboard). 

Finally, select a bad portion and press 'Del' on the keyboard. But if you don't make splits, you'll take out the full video. If you do this accidentally, press 'Ctrl+Z' to undo the deletion.

So for example, let's say your video looks like this:
BBBGGGGGGGBBBBBGGGGGGBBBB

Here B represents the bad portions and G represents the good portions. Play until you are between the first bad/good portion and make a split with 'M'.

BBB|GGGGGGGBBBBBGGGGGGBBBB

Repeat for the next part between the good and bad portion to make another split.

BBB|GGGGGGG|BBBBBGGGGGGBBBB

Repeat for all the places where you need splits:

BBB|GGGGGGG|BBBBB|GGGGGG|BBBB

Finally select each bad clip and delete them using the 'Del' key.

GGGGGGG|GGGGGG

You should end with just the good portions in each clip.