Stroke order of 力 vs 九
About this question, you can consult Guobao Wang's summary:


  1.只有横折钩类与撇相遇：先写横折钩，例刀、力、万 、方、乃、杨。 
  
  2.其他横折类与撇相遇：都先写撇，例如及（横折折撇 ），几（横折弯），九（横斜钩）、匕（竖折弯）。


translate into English:

1.Only when uppermost and rightmost lines with a left hook cross with right-to-left diagonals(ノ): uppermost and rightmost lines with a left hook is written first. For example: "刀", "力", "万", "方", "乃", "杨".

2.In other situation uppermost and rightmost lines cross with right-to-left diagonals(ノ): right-to-left diagonals is written first. For example: "及", "几", "九", "匕".

Anyway, maybe the following links will offer you more information about stroke order rules.

1.现代汉语通用字笔顺规范(official version);

2.现代汉语通用字笔顺规范.pdf;

3.现代汉语通用字笔顺规范;

4.《现代汉语通用字笔顺规范》电子版;

5."火"的笔顺.

Besides, the website 汉典 is perhaps useful to you.