Why Praise was mentioned First

Since the praise of Allah, Who is being sought for help, was mentioned, it was appropriate that one follows the praise by asking for his need. We stated that Allah said,

«فَنِصْفُهَا لِي وَنِصْفُهَا لِعَبْدِي، وَلِعَبْدِي مَا سَأَلَ»

(One half for Myself and one half for My servant, and My servant shall have what he asked.)
This is the best method for seeking help, by first praising the one whom help is sought from and then asking for His aid, and help for one's self, and for his Muslim brethren by saying.

[اهْدِنَا الصِّرَاطَ الْمُسْتَقِيمَ ]

(Guide us to the straight path.)
This method is more appropriate and efficient in bringing about a positive answer to the pleas, and this is why Allah recommended this better method.
Asking for help may take the form of conveying the condition of the person who is seeking help. For instance, the Prophet Moses said,

[رَبِّ إِنِّى لِمَآ أَنزَلْتَ إِلَىَّ مِنْ خَيْرٍ فَقِيرٌ]

(My Lord! Truly, I am in need of whatever good that You bestow on me!) (28:24).
Also, one may first mention the attributes of whoever is being asked, such as what Dhun-Nun said,

[لاَّ إِلَـهَ إِلاَّ أَنتَ سُبْحَـنَكَ إِنِّى كُنتُ مِنَ الظَّـلِمِينَ]

(La ilaha illa Anta (none has the right to be worshipped but You (O Allah)), Glorified (and Exalted) be You (above all that they associate with You)! Truly, I have been of the wrongdoers) (21:87).
Further, one may praise Him without mentioning what he needs. The Meaning of Guidance mentioned in the Surah
The guidance mentioned in the Surah implies being directed and guided to success. Allah said,

[اهْدِنَا الصِّرَاطَ الْمُسْتَقِيمَ ]

(Guide us to the straight path) meaning guide, direct, lead and grant us the correct guidance. Also,

[وَهَدَيْنَـهُ النَّجْدَينِ ]

(And shown him the two ways (good and evil)) (90:10), means, `We explained to him the paths of good and evil.' Also, Allah said,

[اجْتَبَـهُ وَهَدَاهُ إِلَى صِرَطٍ مُّسْتَقِيمٍ]

(He (Allah) chose him (as an intimate friend) and guided him to a straight path) (16:121), and,

[فَاهْدُوهُمْ إِلَى صِرَطِ الْجَحِيمِ]

(And lead them on to the way of flaming Fire (Hell)) (37:23). Similarly, Allah said,

[وَإِنَّكَ لَتَهْدِى إِلَى صِرَطٍ مُّسْتَقِيمٍ]

(And verily, you (O Muhammad ) are indeed guiding (mankind) to the straight path) (42:52), and,

[الْحَمْدُ لِلَّهِ الَّذِى هَدَانَا لِهَـذَا]

(All praise and thanks be to Allah, Who has guided us to this) (7:43), meaning, guided us and directed us and qualified us for this end - Paradise.