As you wish - it is generally 'ok' to open attachments if you follow a few simple rules:
1) You do have a good AV programme, regularly updated?
2) Are you expecting it?
3) Does it 'sound' plausible?
4) BEWARE "here is a mobile photo for you click the attachment to view" stuff - I always check with supposed sender first.
I have no doubt others will add warnings/caveats, but these are the basics. NB Any attachment can carry 'infectious' code.