Street photography comes with a lot of constraints on equipment and methodology – no diffusers, no reflectors, no asking people to please move one way or the other – so the best advice is to concentrate on what you can control: where you shoot, and how you shoot.
Much of this boils down to know your city, or be ready to explore it. Interesting compositions can make up for technical deficits, so find interesting places and concentrate on those.
Watch where the shadows fall. Midday at summer will always be problematic, but there are always awnings, bridges and overhangs to take advantage of, and tall office blocks almost always have a shaded side. As soon as the shadows get a little longer, they can benefit you in a lot of ways. A background in shadow with the subject brightly lit can be a strong composition. The transition from shadow to sunlit space can be very interesting, objects like signposts can cast interesting lines, and large blocks of shadow can make some interesting geometry, for example:
Watch for reflected light. This can be something as extreme as No Flash Corner, or as simple as an interesting pattern or unexpected contrast in an otherwise-shaded area. There are almost certainly some 'sweet spots' for reflections at various times of day. Tall office blocks can cast reflections of their windows even at midday.
Exposure and postprocessing
If you don't already, use a hood. This will help eliminate any possibility of veiling flare (I think these printable hoods are always worth mentioning). Similarly, it might be worth removing any 'protective' filter if you habitually use one, if only to rule it out as a source of flare.
Underexposure can help by improving colors, but also make sure you're metering the right thing to begin with: the street/sidewalk/people, and not the sky.
White balance may also need some slight adjustment; slight blue casts (from a white balance set too low) can really rob from the apparent detail of an image. Alternately, give a warm tone to highlights to separate them from the cooler shadows.
Some street photographers use fill flash, but it definitely is more intrusive, and isn't a technique (or a look) that everyone likes. I think anyone concentrating on street should give it a try, but it might not be a long-term solution for you personally.
Of typical filters, graduated NDs just aren't compatible with typical street compositions. Haze and UV filters have a minimal effect on nearby subjects. Polarizers could be useful, though you should avoid the temptation to fiddle, or you'll likely end up missing shots – I'd try to preset it to something reasonable for the area you're shooting.