Trying to get into the 145 club hey Chi?
Seriously though mate, I think you're doing everything right at this stage, all you need to do is get some depth training. I know already you're pretty comfortable in the water so the areas I would suggest you need to look at are equalisation, weighting and deepwater technique.
Buoyancy - for a 40m dive i'd be looking at being neutrally buoyant at around 13-15m.
Deepwater technique - based on being neutral at 13-15m i'd be kicking down to about 10m and slowing my kicking down over the next 20m and by the time I hit 25m would stop kicking altogether and let the negative buoyancy take you down the rest of the way. This is by far the best part of the dive!
Equalising - keep your chin tucked into your chest the whole way down. Equalising will get quite hard somewhere after 25m, so a lot of people learn the Frenzel/mouthfill method of equalising, do a search on the forum for the Frenzel document to learn this. The idea is to fill your mouth with air before your lungs shrink so much that you can't bring up air from them (for me I do a mouthfill at around 25m), then use this air for the rest of the dive to equalise with.
Don't try and go from 20m to 40m in the space of a day, put a few metres on each day and let your body get comfortable with the different feelings/pressures.
There are some exhale exercises you can do but i'd strongly suggest you grab Nathan Watts and head down to Shelly beach for those as they are advanced and can be dangerous if you're not careful, plus they must be done under supervision.
Search around the forums, there's a ton of info already here.
Have fun and i'm sure you'll be hitting impressive PB's out there in Hawaii. Who are you going out there with?
Cheers mate,
Ben
