Experienced drivers know that the roads are safer and more efficient when everyone follows a few common courtesies and basic rules, and this also applies in the pool.
The event swim is a zig-zag, so you have to go under the lane ropes. If you can dive smoothly under the rope during your turnaround, rather than stopping and ducking under it, it'll make your swim much faster.
There will be swim marshals observing and directing slower swimmers to let others past. If a marshal believes you haven't given way when asked and you are holding up the lane, you will be shown a Give Way sign. You must stop at this point to let other swimmers past: if you ignore this you will be given a time penalty.
If you catch the person in front of you and want to overtake, you should gently but distinctly touch the feet of the swimmer in front. It may take two or three touches, but overtaking swimmers should not need to repeatedly slap or grab at the legs of a slower swimmer to politely make their presence known.
A lead swimmer who feels a touch on their feet from an overtaking swimmer should continue to the lane end, then stop in the corner of the lane to let faster swimmers past. A single light touch may be accidental and can be ignored, but two or more distinct touches should be regarded almost universally as a request to swim through.
Swimmers enjoying a draft behind a strong lead swimmer but who are only just able to hold that pace should think twice before tagging the leader's toes and requesting to move ahead. In such situations, it's highly unlikely that the (formerly) trailing swimmer will be able to hold the same pace for very long when leading without the draft. This can lead to repeated 'leap-fogging' and unnecessary contact, which can be annoying and disruptive for everyone in the lane.
Drafting swimmers not wishing to pass should swim far enough back from a lead swimmer that they don't inadvertently touch the lead swimmer's toes.