Every publication has mechanical ad specifications due to the fact that the publications run on high-speed web presses that have certain print limitations.
For instance, there will be a minimum text size (probably around 7 point) and minimum text size that will successfully reverse (maybe 10 point.) Other considerations that will help your ad to print correctly:
Max of 300% is common.
For example, a color panel of 100c, 100m, 60y and 100k = 360% will have too much ink coverage and will not absorb into the paper and simply smear across the sheet.
Text of 12 point size or smaller should be built of solid color and not of tint screens which will appear blurry.
Build a “rich black” of 30c, 30m, 30y and 100k for good coverage to ensure your solid black doesn’t look washed out.
Keep all critical imagery, text, and logos about 1/2 inch in from the magazine’s trim to avoid undesirable effects.
Always review the publication’s ad specs prior to layout for best print results.