In any fluxing process, (Such as FCAW) you need to keep control of the slag. In general, it can lead to problems if you have the slag running in front of your weld puddle to any great extent. For this reason, in the flat position, you should point the arc in the direction of the weld that has already been laid, not in the direction of travel. (I get mixed up whether this is a push or pull angle.)

In the case of GMAW, you would typically hold it in the opposite direction.

Hope this helps

Regards
Niekie Jooste

Dutch,
The push or pull angle isn't all that critical, as long as the angle isn't too excessive. Using a push angle(pointing in the direction of travel) seems to preheat ahead of the weld pool, and gives a flatter bead profile. The pull angle (pointing back into the weld pool) gives a deeper penetration, but a more slightly "humped up" bead profile.
The push angle does seem to force some slag to run in front of the weld pool, but if you have a good re-entrant angle(a smooth blend joining the toe of the previous bead into the base metal) concerning the previous weld beads, then I wouldn't think that you'd have much of a problem, as long as you maintain a fairly high travel speed. Pushing also seems to give a higher incidence of undercut and underwash( similar to undercut, except there's not a sharp transition from weld metal to base metal at the toe of the weld, just a reduction in thickness).
Either angle is acceptable, as I said, as long as your torch angle doesn't get too excessive, say + or - 10 degrees, and you keep the wire burning on the leading edge of the weld pool.
As with all welding, it is situation dependant. Both pushing and pulling have pro's and con's. It mostly depends on what your trying to do.
Hope this helps.
Dale Simonds