Just an FYI, I weld professionally daily. most smaller welders will generate allot more spatter, they do not have the power to get the penetration. if it is very bad try to adjust the wire feed down till it goes away. Weld anti-spatter spray does work wonders but it should be used in a well ventilated area as the chemicals in it are very bad for your health.
All welding should be done flat or uphill, never weld downhill or you will get a weak weld with slag intrusion. When welding uphill point the nozzle upwards to push the weld up. When welding with flux core you should drag the weld, point the weld nozzle where you have been not where you are going. you do not need to lean the nozzle way over, almost pointed straight in is ok. with solid wires you should push the weld, point to where you are going. the same apply's for the angle of the nozzle, you don't need much.
One last thing, you want to point the nozzle straight into the work, this is hard to explain. consider two pieces of steel laid flat, the seam need to be welded. you want to point the nozzle straight down into the seam then lean it whichever way you need, depending on the wire you are using. same would be true for two pieces on a rite angle, you would want the nozzle to be pointed straight into the joint then leaned in the rite direction.
Hope this helps