How to pitch the additional service?

Hi guys,

Small bit of advice needed here.

I have been offering copywriting services for the last two years. Recently I have been studying SEM, and feel I can give quality advices on the subject.

My question is the following: How do you go about suggesting an additional service to a regular client?

Per ex. I have this client I do regular copywriting for his webpage, and I am sure his site could need a bit of optimization and keyword placements.

My concern is not sounding too agressive, as I dont want to lose the copywriting services altogether.

Any advices?

Thanks for reading me :)

Dave