ACAS1207:
but want to go on a few other trips to 'practice' diving because I have read that there are strong currents and it's no place for novice divers.
You've already started to get some good advice, but more to your question: Tobago, specifically Speyside area.
Your desire to get similar diving is sound, but your question lacks details, Exactly how will you be doing the Galapagos? That information is key as to the conditions. Liveaboards vary from ship to ship, land based is different as well.
"Advance Diving" is merely one and more new situations presented individually or piled on top of the other.
Advanced diving in the Galapagos could mean:
-Negative entries (as mentioned above) with quick descents
-Ability to play the currents to stay with the group
-Recognizing a "downwelling" and quickly reacting to it.
-Understanding how to shoot your sausage from depth and waiting patiently at 15 feet for the boat to pick up.
-Handing your gear up safely, efficiently and quickly to the boatman, then scrambling aboard. Using up little space when on board.
-Surface signalling and rescue skills. Preparation for a very unlikely long float on the surface
-New thermal protection levels as well as weraing work gloves to grab onto the lava flow rock.
.... and a few hundred other things. I have seen relatively inexperienced divers do well, I have seen divers with 1000 dives (under varyingly different circumstances) need to be hauled out and toweled off.
Tobago offers small boats as well as lateral and vertical currents. Good experience, but even there- ask the DM for assistance and advice.