Since you say that you are using one stage of an LM358 (presumably operated from a single rail supply), put the anti-aliasing filter between the level shifter and the ADC input. If the DC level is right for the ADC now, it will be right for the anti-aliasing filter, too.
Use a two-pole, unity gain, low-pass Sallen-Key filter like the one shown below. I used 10Hz as the cutoff frequency. If you want something else, download the free program from the TI website, and recalc.
ps, I just saw the other thread about the level shifter. Put the anti-aliasing filter ahead of the level shifter. That way, the range of the signals through the anti-alias filter is guaranteed to stay between 3.5 and 5V, which is well within its common-mode range.
Also, to enable the level-shifter to pull all the way to ground, without the slight non-linearity shown in Eric's LTSpice sim, put a 10K resistor from the output of the level-shifter to ground, effectively in parallel with the ADC input.
This is one case where I wish you hadn't started a new thread. If I had seen the original thread I would have come to the correct solution much easier...