Rammus is an early game ganker. Make sure you have wards in the river or at his jungle entrances to reduce the effectiveness of his ganks.
He doesn’t have the healthiest first clear. If you’re a strong early game champion, try to invade him on his first clear to set him behind from the get go.
Rammus will activate his Q quite close to a lane but outside of general warding spots to make it harder for the enemy to escape. Place slightly deeper wards rather than warding usual warding spots to give you more time to escape.
Team fighting can be difficult for Rammus as most players will disengage as soon as he runs towards them. This means Rammus will probably try to flank you in team fights so he can get on a high-value target.
If you’re a carry, invest in a Quicksilver Sash to escape his taunt E so he is unable to target you in a team fight.
Make sure you group as a team and avoid splitting up too much as Rammus will try to pick off and start a fight when teams are split up.
From level 2 onwards, Rammus can gank with his E. If you know where he started, he may try to level 2 gank mid or try to level 3 gank the opposite side of the map.
The longer the game goes, the tankier Rammus becomes. Make sure you get magic penetration items for AP champs and armour pen for AD champs.
Once Rammus hits level 6, he becomes more of a nuisance as he will now deal more damage when he ganks. Play respectfully and avoid overextending post 6 to reduce his chances of visiting your lane.