When to visit?
As far as weather is concerned, any time of year is a good one to visit Raja Ampat. Climate and underwater conditions are good all year round - there isn't really an "off-season".
Sea travel in smaller boats can be problematic in June, July and August, so if you plan on covering a lot of ocean it would probably be best to pick a different time of year.
If you just want to relax in a tropical island paradise and do a bit of snorkelling or diving around your chosen island, then any time is great.
How to get here?
Arrange (before you arrive!) with your host to pick you up from Sorong.
If you want to go it alone: