My only advice to add to Fabbrisd 's solid comment:
I did mine with the valve stem parallel with the ground (3 o'clock or 9 o'clock.
I put paper towels on the rim to catch any drips to make clean up easier.
A few Q-Tips were kept handy, to swab out the inside of the valve stem, before screwing the Schrader valve back in.
Spin the tire some to re-distribute the sealant. Even better, take it for about a 1 mile ride.
At first you may feel the tire is slightly out of balance; this will smooth out as the sealant distributes evenly inside the tube.
I am a huge fan of the Flat Out product.
My tube had a leak which resulted in a flat tire in 12 hours (from full pressure to 2.5 PSI in 12 hours). Goathead thorns are bad in my area.
I did not patch the tube, only flat-out was used.
Flat out sealed the tube after a quick jaunt riding the bike.
No air has been needed to top it off in over a week.