Estes Hex-3, #7263, Build, Part 3, Scoring The Fins

The instructions say to fold the fin lines over a straight edge. I don't see how this could be successful unless you have a very thick straightedge.

You'll get much cleaner folds if you pre-emboss the fold lines.

I did my usual embossing before the fins flats were cut off the full sheet. Trust me, it's easier to emboss when the fins are still on the sheet.

I used the un-serrated, smooth thin tip of a butter knife. Set a straight edge down the line, allowing a little space for the thickness of the knife. 

TIP: If you emboss over corrugated cardboard, be sure the inside ribs of the cardboard run parallel to the lines you are embossing. 

This is the back, unprinted side of a fin.

Look close and you can see the embossed lines.

Don't just do a single, sharp fold - 

Work up to a sharp fold line. Coax the tab folds little by little and finish with a sharp crease with a burnisher.

Odd'l Rockets Cutaway Engine Build, Part 3, Rounding Over End Folds

The end cap on the left has been folded.







Fold the triangles under with your fingers first.
The triangle corners can be rounded a bit more by rolling over the corners with the burnisher.






Round out the small bent back corners for a better fit in the end of the half body tube.








Fold the side flaps back on the large engine face print.

Fliskits Pheord X150 Build Part 5 Shroud Scoring

Step 9 has you cut out the shroud. 
You might find it easier to make the score lines before cutting out the shroud.

Step 10 has you cut halfway through the fold lines in the shroud.
A prefer to do a "blind emboss" on the score lines with no cutting.

The backside of a single edge razor blade works well for this. You could also use the non-serrated area of a butter knife.
Put plenty of tape layers over the sharp blade edge so there is no chance of cutting your fingers.
The rolled over metal "top" of the razor blade is flipped over and pressed down. Run the smooth rolled edge over the fold lines.
Don't press too hard, you don't want to scratch the print.

To get a cleaner crease, the straight folds were pressed over a straightedge ruler.