Trouble sinking...I definitely had that one early on. Instead of helping me with my technique, the instructors and DMs just loaded me up with more lead. Not cool for shore diving.
Tips? Refer to your OW manual and calculate the weight you need for your weight and exposure protection. At most you might need 5 more lbs than that to get started. In the water, when you’re ready to descend hold your BCD LP inflator hose high, straight up, and press the button to release the air, while exhaling completely.
Masks...a few tips. If brand new, you should have "scoured" the inside surface with toothpaste and then rinsed well before the first use. If you haven’t done that, do it now. When actually diving you can use commercially available defog solution: spread it on the inside surface of the lens and then rinse well shortly before donning. I always carry a small bottle of conditioner, or shampoo, or dish soap to squirt on the ankles/wrist of the wetsuit to help me slide in more easily, but I’ll use this as defog in a pinch as well.
In a few cases people still have a problem with fogging, supposedly because the silicone skirt can retain some sort of coating as well; I’ve heard that washing the skirt well with warm water and soap fixes the issue.