What to look for in employee share deal/equity arrangement?

We have recently completed a 3 month trial (as consultants/devops) with a startup who had raised around $1 million before we got on board (valuing the company at around $2.5 million).

We are happy working together and have been in discussions as to our compensation and have come to the number of between 3% and 8% of the company as a fair figure for our contribution.

The one thought I have is how does this work if they raise more money - everyone will get diluted - which is fair enough. If they raise another $2.5 million, I guess we get half of what we initially agreed on. Is this correct?

Has anyone got any other recommendations for things to look out for? (I'm most worried about the Skype type thing, where they end up with nothing).

We will see a lawyer to get this drawn up properly but we are kind of in the middle of nowhere and lawyers here may not have a good understanding of this kind of thing.