> As the front and back surfaces of the paper, as determined during the papermaking process, differ slightly, one side is preferred as the side to image first. The primary determinant of which side to print first is the paper’s curl characteristics.
> If you are using a quality paper intended for digital printing, the ream wrapper will be marked with an arrow that points to the preferred printing side. Print on this side when printing one side only; print this side first when printing on both sides of a sheet.
> Whether this side is to be loaded UP or DOWN in the paper tray has to be determined for each machine (and sometimes for each paper tray) by reading the system's operator guide. Once you've determined the correct orientation, marking each paper tray with a label indicating the correct loading direction helps avoid operator error and lost productivity.
> Determining Curl
> In the event a paper ream is not marked for correct print-side orientation, it may be necessary to determine the curl direction yourself. Do this by holding a 1/2-inch stack of paper by one of its short edges (refer to figure 4-2). Let the paper hang with the long edge parallel to your body. Either the lower edge or the two side edges will be curling slightly toward the center. Observe which way the edge(s) curl. This is the curl side. Load the paper into the tray such that the side opposite the direction of curl is imaged first.
> Note: If the ream had an arrow marking, it would point to the OPPOSITE side. Load into the paper tray in the appropriate direction
> Built-in Curl
> Xerox papers are manufactured with a small amount of “reverse curl,” so that they will be very close to flat after processing – this will facilitate any post-processing that needs to occur, such as binding, trimming or folding. Load according to the arrow direction for best results.
> Loading The Paper Tray
> Carefully unwrap the reams of paper to be loaded, taking care not to bend any of the sheets or otherwise damage the paper. Inspect the paper for any obvious signs of damage (bends, folds, crumpled or wavy edges, tight edges), or defects. Fan the paper as necessary to avoid sticking edges. Do not handle the paper any more than necessary.
> Load the reams into the paper tray one at a time, taking care to observe the correct orientation, as indicated by the ream wrapper arrow.
> When more than one ream is being loaded, it is important to make certain the reams are aligned atop one another. It is easy to wrinkle, bend, or otherwise alter the top sheet of a lower ream when placing another one on top of it. The interface between reams in the paper tray is a frequent source of jams. It is particularly important to avoid loading successive reams inconsistently (some arrow up, some arrow down).
> Observe the paper fill line marked on all paper trays and do not load paper above this line.
Paper has a right-side-up, and your printing life improves drastically if you just look at the little arrow before putting the paper in the printer.
https://www.xerox.com/downloads/gbr/en/p/Paper_Guide.pdf
> As the front and back surfaces of the paper, as determined during the papermaking process, differ slightly, one side is preferred as the side to image first. The primary determinant of which side to print first is the paper’s curl characteristics.
> If you are using a quality paper intended for digital printing, the ream wrapper will be marked with an arrow that points to the preferred printing side. Print on this side when printing one side only; print this side first when printing on both sides of a sheet.
> Whether this side is to be loaded UP or DOWN in the paper tray has to be determined for each machine (and sometimes for each paper tray) by reading the system's operator guide. Once you've determined the correct orientation, marking each paper tray with a label indicating the correct loading direction helps avoid operator error and lost productivity.
> Determining Curl
> In the event a paper ream is not marked for correct print-side orientation, it may be necessary to determine the curl direction yourself. Do this by holding a 1/2-inch stack of paper by one of its short edges (refer to figure 4-2). Let the paper hang with the long edge parallel to your body. Either the lower edge or the two side edges will be curling slightly toward the center. Observe which way the edge(s) curl. This is the curl side. Load the paper into the tray such that the side opposite the direction of curl is imaged first.
> Note: If the ream had an arrow marking, it would point to the OPPOSITE side. Load into the paper tray in the appropriate direction
> Built-in Curl
> Xerox papers are manufactured with a small amount of “reverse curl,” so that they will be very close to flat after processing – this will facilitate any post-processing that needs to occur, such as binding, trimming or folding. Load according to the arrow direction for best results.
> Loading The Paper Tray
> Carefully unwrap the reams of paper to be loaded, taking care not to bend any of the sheets or otherwise damage the paper. Inspect the paper for any obvious signs of damage (bends, folds, crumpled or wavy edges, tight edges), or defects. Fan the paper as necessary to avoid sticking edges. Do not handle the paper any more than necessary.
> Load the reams into the paper tray one at a time, taking care to observe the correct orientation, as indicated by the ream wrapper arrow.
> When more than one ream is being loaded, it is important to make certain the reams are aligned atop one another. It is easy to wrinkle, bend, or otherwise alter the top sheet of a lower ream when placing another one on top of it. The interface between reams in the paper tray is a frequent source of jams. It is particularly important to avoid loading successive reams inconsistently (some arrow up, some arrow down).
> Observe the paper fill line marked on all paper trays and do not load paper above this line.
There's a bunch more there about correct storage.