Every race is totally different.
Aiming for the marathon is a task of sorts which can include terrific highs and lows.
I believe you'll develop speed via strength work which includes hill running, either repeats, or running hilly courses as the Kenyans do on a steady basis
Being a lifelong runner, knowing what running gives me, a variety of factors - that is what motivates me.
No one who works a forty hour week will ever beat me.
The advice I have for beginners is the same philosophy that I have for runners of all levels of experience and ability -- consistency, a sane approach, moderation and making your running an enjoyable, rather than dreaded, part of your life.