Firstly, make sure you're using yeast that has not passed the expiration date. If you're finding chunks of yeast, you may want to check the dough during the knead cycle and hand knead a bit to make sure it is well combined.
How to add your yeast depends on two things, 1) what type of yeast (instant or active dry) and 2) when you plan to start your kneading cycle.
If you're kneading straight away and using Instant yeast, it doesn't matter what order you put the yeast in. Instant yeast has smaller particles, so it may mix in more easily as well. If you're using active dry yeast, it may be better to add the yeast and sugar to the water first to dissolve and activate before you add all of your other ingredients. The water should be at about 110 degrees F and the yeast-water mixture allowed to proof for about 10 minutes. If it gets all bubbly and foamy, you know your yeast is good and it's ready to go.
If you plan to use a delay timer, add liquids first, then flour, then yeast on top to keep it dry.
If you're still not getting good results, you may want to increase the amount of yeast or decrease the amount of salt. Salt (or too much sugar, like in sweet rolls) will inhibit yeast growth. The general rule is 1/2 tsp salt per cup of flour. You can also add 1Tbs of an acid like vinegar or lemon juice to give the yeast a jumpstart. Hope these tips help you out!