I`ve used this a lot. Its really drawing, but I`ll try to explain it to you.
First for right turn holdings: Divide your DI or HSI up in the following (clockwise):0-70 deg Teardrop, 70-250 deg Direct and 250-360 Parallell. Place your OUTBOUND holding course in either of the sectors and you`ve got your entry. For left turn holdings its the opposite. 0-110 Parallell, 110-290 Direct and 290-360 Teardrop.
Please correct me if I`m wrong, and please dont call Teardrop for Offset entry (even if JAA discovered flight).
Good luck