One would think that a yellow line in front of you should be a clear indication that you are still on a taxiway, but
when confronted with signage that isn't exactly clear on directions,

FAA signage is limited and rather clear. If you have problems reading
it, you should study your AFD or airport diagram BEFORE entering the
movement area, or find an instructor or experienced pilot to help you.
You can have all your FAA regs and definitions down pat, but, a pilot
who can't interpret the signs or stay on the taxiway is dangerous.

Other than the AIM, which is obvious, here are some great resources
for students and other pilots:

http://www.faa.gov/airports/runway_safety/quiz/ -- FAA
material.
http://www.aopa.org/asf/publications...RWcards_lo.pdf --
AOPA flashcards. The FAA distributes these as well.
http://www.airnav.com/airports/ -- Airport diagrams

A professional pilot will have studied the airport diagram and will
already be familiar with the most likely routes to the active runway,
or to parking.

Usenet flamewarring aside, the local example which could confuse
anybody is Paine Field in Everett, WA. http://204.108.4.16/d-tpp/0909/00142AD.PDF
Runway 11/29 appears narrower than the alpha taxiway and ramps, and
not all the taxiways are marked on the diagram. Also notice that 29
just sort of starts in the middle of the tarmac. You're taxiing along
on what seems like a sea of asphalt with hangars in the middle of it,
and all of a sudden there's a runway. For an unfamiliar pilot,
especially one who comes in at night or in bad weather or is fatigued,
it's easy to be on the yellow line and still get lost. I requested and
received progressive taxi, but I'm pretty sure there are places there
that the ground controller can't even see you.

for me, I lose that yellow line in front of me trying to figure out, ok, which way do I turn especially when multiple taxiway entrances and
exits are there.

"What kind of ..." :P

These problems are common, and exacerbated by fatigue and stress and
also fear of making a mistake.

-c