Smash 3 Burnout Billboards
Drive through any three of the 120 billboards in Paradise City. To the south of the junkyard where you start, there are three billboards across the center divide in the road. All three are extremely easy to get to.

Smash 30 Burnout Billboards
Smash through any 30 of the 120 billboards in Paradise City. Some of these are difficult to get to and require some long jumps, but most are pretty easy. The Smash 60 Billboards trophy has a map showing the location of all 120 billboards.

Smash 60 Burnout Billboards
Smash through any 60 of the 120 billboards in Paradise City. Since you only have to drive through half of them, go for the easy ones. Here is a map showing all the locations of the billboards.
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Drive through 10 sets of Yellow Smash Gates
Smash through 10 of the 400 yellow gates. These are the fences with yellow signs that block alleys, car park entrances, short cuts, construction sites, and little side roads. 10 gates are extremely easy to find so there is no need for a picture but there will be one for the 200 gates trophy in a different tutorial.