Choose the Right Weight:
Sometimes, and especially when you are new, it can be difficult to figure out how much weight to lift. If you are not experienced in the weight room, the easiest way to know and usually right away is to grab a weight with which you can perform 10 reps.
If you can do more than 10, that is your sign too add a few more lbs.
If you can't get 10, go for lighter weight. That would be your 10-rep max.
Then use that info to determine what weight to use for the reps in your workout.
If you can lift 15 pounds for your 10-rep max doing a bicep curl and your workout calls for 8-10 reps per set, just take 60-80% of your 10 rep weight. For this example, you would use between 9-12 pounds. Round to nearest weight available if needed.
THEN, set a goal to increase the weight as you progress down the road. Our bodies are very smart and will adapt if you let it. If you let it adapt, then not much change will occur. So force your body to work beyond what it is capable of.