so glad u came on here with this. i love lofi and i always have. theres many different ways, some of the most effective being a bitcrusher to literally lower the quality of the sample, using high cut shelves on an EQ to give it less of crisp sound, using overcompression tactfully and adding slight distortion. try putting vinyl fuzz samples underneath all your beats, that can add more of a lofi feel as well. i'd be glad to answer any questions you have if u wanna scroll thru my beats, i use a bitcrusher and smart overcompression on pretty much everything cause i love the dirt and the grit. even this beat :
although, with that one it is more slight. if u wanna scroll thru my beats and see if any of them have the sound youre looking for i would be more than happy to tell u what effects i applied to get that certain sound. love to ya homie and best of luck.