Q: I have 2 problems with my weight training.
a)There are some kind of exercises that are secondary.As ppl at gym told me purpose of these arent to up the kgs a lot but these are supposed to help me improve specific parts of my body in order to be able to do better in time other exercises that are considered to be main.If i do first the main exercises(hard ones) iam too tired to do the secondary ones after and this goes vice versa.Ppl told me to do the main exercises first as hard as i can and with the remaining power after to do the secondary ones with reducing the kgs if necessary.What is your opinion?

b)In some exercises the sets go strange.Iam supposed to up the kgs after i can hit more time then 12 in my first try.So,i lift 80 libres at a machine(before i did 12 reps in 70 and now i do same in 80).I can do 10 at 90,but cant do 8 at 100.I do 6 like before.What kind of reps would u suggest in cases like these?

A: For a) I agree with the advice you received. You should do big compound exercises with freeweights like squats, lunges, deadlifts, presses, rows, and pullups/pulldowns first before moving on to other 'smaller' exercises like machines or cables work or arm exercises.

For b) I am not sure I understand your question exactly, but I think you're doing everything right. You should increase the weights once you can do more than 12 reps in a row. So, for example, if you've been doing 3 sets of 12 reps at 70 lbs relatively easily, then you should increase weights to 80 lbs and do as many reps as you can in every set. You might be able to do 12 reps at 80 lbs in the first set, 10 reps at 80 in the second, and only 6-8 reps at 80 for third. If you wanted, you could even try heavier weights than 80. So you might do 12 reps at 80 for first set, 6 reps at 90 for second, and 5 reps at 90 for last. So, basically, you can mix and match weights as you like, just as long as most of your sets you can't do more than 12 reps. Hope that helps!