There’s various considerations and preparations before you’re even in the water:

• equipment 
• buoyancy control device (BCD) – this is like a life vest that deflates and inflates at the push of a button. Controlling the amount of air in this helps maintain neutral buoyancy (the weightless state) since the pressure of the water changes how you float / sink. Most things then attach to the BCD including a backup regulator and pressure gauge. At my level, it is also what my tank attaches to.
• air / nitrox tank – obviously you need to breathe somehow…
• regulator – this is the piece that goes in your mouth and attaches to the tank so you can breathe underwater. It always reminds me of a Star Wars character.
• mask – this needs to fit well, hair can’t be caught in it and cleaning it with baby shampoo or some anti-fog mix and spit before diving seems to help it to stay clear. I don’t enjoy taking my mask off underwater or clearing it since I rarely seem to be able to get that last drop of water out that likes to sit right beneath my nose. It annoys me.
• fins – these are handy to make it easier to swim
• weights / weight belt – not because it’s easier to work out underwater but because I tend to float away as my tank becomes lighter. More so in very salty water too. I’m improving in this area but still needed. There’s many schools of thought on this. I’d prefer to use them and know that I will be able to hover at my safety stop for the time that’s needed.
• wetsuit – no matter how tropical it is where I dive, I always wear one and usually a wet shirt too. This is because the human body is pretty clever in that it likes to try to match the temperature of the environment it is in. Deeper underwater is cooler and the longer underwater, the more my temperature drops. I am not a cold weather person. Unless I’m skiing and am rugged up. This is not appropriate clothing to dive in though and would be quite restrictive.
• colour – in spite of what one of my friends who is an incredibly experienced diver thinks, I am yet to see a reason why everything should be black. He maintains that it looks cool and that’s how people know you’re a professional diver. I don’t want anyone thinking I’m professional, that would produce unwarranted performance anxiety, so I figure I should wear as bright as possible. To put this in context, he’s the kind of guy who dives in the dark, with two tanks, leaves trails of rope so he can find his way back with his dive buddy and is comfortable diving in silt so he can “see” some wreck that most of the rest of us recreational divers would miss. He’s also quite comfortable with diving in caves where he can’t see anything and the only way to tell which is up, is where your bubbles are going. This can get mixed up in turbulence though… Yes, he’s hardcore. I’m not. This comes back to knowing your limits. And I like bright colours.

• safety
• all this equipment has different things that can go wrong with it which you check it before each dive
• descending – main part to watch out for here is the pressure on the ears. As part of getting your diving licence, we’re all taught how to equalise safely and to go up a bit if needed
• ascending – there is a fixed rate this needs to be done at to avoid the bends. There’s also a compulsory safety stop at the end of each dive. General rule of thumb for my level of diving (I’m an inexperienced recreational diver) is about 5m for 3-5 minutes.
• dive plan – know how long, depths and general course you’re going to be following
• breathe – normally and never hold your breath
• flights – no flying until 24 hours since my last dive. This is a very conservative measure compared to some but I’d prefer safe than in a decompression chamber or worse. Good reminder to sort out diving insurance too…
• buddy – always dive with someone else as you never know. I’d prefer to look at this as having someone to help me spot nudibranches since two pairs of eyes are definitely better than one.
• never dive beyond your experience level. As tempting as it might be to do something really cool, if I’m not confident or the conditions are more than what I’d feel safe doing, the answer is no. There will be other dives!
• training / licence – everyone that dives should do this. It gives you the skills and starts to build confidence. It teaches what to do when things go wrong underwater including buddy breathing.
• don’t touch anything – it could be poisonous, it could be essential to the ecosystem. Nature balances, let it balance without interference.

With all of these things to think about, you’re probably now thinking “why bother?”. 

That’s easy:

• total bliss
• stunning wildlife
• being neutrally buoyant feels like what I imagine to be being in outer space. A night dive adds to this feeling significantly as the sand (assuming you’re diving over sand) takes on a moonscape look and all other sorts of creatures come out at night.
• underwater exploration to spot favourite, different, unique animals and wildlife. Fun challenge!
• feel part of something so much bigger than the day-to-day
• actually spotting something that you’ve been looking for that is difficult to find. I’m thinking specifically about those pygmy seahorses, that are smaller than the size of a fingernail. Spotted at Anilau, Batangas, Philippines. Seeing my first manta ray in the wild was also pretty cool, as are turtles and my favourites, the nudis….
• being able to travel and meet others who recommend specific spots. My latest at Tulamben was suggested to me by a woman I’d dived with in Hawaii. Yes, my life is rough at times. 
• improving – I like to practice with my buoyancy and see how I can be better at controlling where I sit in the water by breathing differently
• focus – to be totally absorbed in the surroundings with no thoughts of anything else but what I’m seeing and doing
• no email

* Thanks to Felix Da Housecat for the title to this post.