Top foliage becoming small, often twisted - Two possibilities here; damage from herbicides, either in the planting medium, or more likely, drifting onto your plants from nearby lawn treatments, or viral infections spread by insects such as leaf hoppers, white fly or cucumber beetles. The plants can often withstand the former (especially if new growth, such as shown on suckers or developing side shoots, looks OK), but will succumb to the latter.
Lower foliage developing brown patches and spots, perhaps with some yellow coloring - most often this is a fungal infection called Early Blight (also known as Alternaria). It is common, surviving in garden debris or soil, and gets onto plants by splashing onto lower foliage. It is really important that tomato foliage remain dry (unless it rains, of course - nothing can really be done about that), so water from below. Ensure that the sun can shine on as much of the foliage as possible, and that air can circulate around the plants. Mulch below the plants so that soil can't splash up onto lower foliage. Remove lower, infected foliage, either snapping it off. or using shears - but disinfect the shears by dipping in rubbing alcohol when moving between plants so you don't spread the issue.
Some foliage is curling and it varies throughout the day - physiological leaf curl impacts different varieties differently - most not at all, some very noticeably (varieties like Rosso Sicilian and Costoluto Genovese have a genetic tendency to curl their leaves). As long as the foliage is green and you don't find insects - white fly or aphids - sucking on the back sides of leaves, it isn't a concern.
Dark brown or black patches showing up on the bottoms of young tomatoes - blossom end rot is a real problem for tomato lovers, often striking the first few fruit, even more paste varieties, and those that are in containers due to it being harder to provide sufficient, even watering. If you are growing in containers, have bottom holes and using a nice soil less mix augmented with compost, you can't over-water. If plants have lots of small green tomatoes, allowing them to wilt during the hot part of the day can lead to blossom end rot. I am actually watering my bale and grow bag tomatoes morning and mid day!
What else is troubling your tomato patch? Email me and let me know!