Warnings may be issued by moderators or administrators if a user has violated one or more of the Forum Rules.
Generally, behaving like in real life is the best way to avoid one's warning-level to rise up, but in case this fails, here is the listing of applicable warnings with their respective severity:

Follow the Rules
Just a reminder to check the forum rules again; no increase in one's warning level.

Rule 1: Think before posting
+10%, 2 weeks

Rule 2: Etiquette
+30%, 2 weeks

Rule 3: Follow posting guidelines
+10%, 2 weeks

Rule 4: Follow profile guidelines
+10%, 2 weeks

Rule 5: No multi-accounting
+40%, 3 months

Rule 6: No backseat moderating
+10%, 1 week

Rule 7: English only
+10%, 1 week

After the specified duration, the warning level will automatically decrease by the amount that was given before. However, please keep in mind that, after reaching a certain level, it is possible to receive a penalty:

20% - Moderate new posts for 1 Day(s)
30% - Moderate new posts for 2 Day(s)
40% - Suspend posting privileges for 3 Day(s)
50% - Move to banned group (Banned) for 3 Day(s)
70% - Move to banned group (Banned) for 1 Week(s)
90% - Move to banned group (Banned) for 2 Week(s)
100% - Move to banned group (Banned) Permanently

Additionally, a moderator or administrator may define a custom reason (with its very own parameters) to warn you. If you keep the forum rules and general netiquette in the back of your head, however, there is no reason to warn you. Be friendly, polite, and enjoy your stay here.