I took French for years and had difficulty with my pronunciation. I haven't taken it in 23 years and it turns out the same is true now. Duolingo isn't quite enough for me to keep up with it. Does anybody have any tips or tricks on how I can improve?
Pimsleur is not free - but your library might have it. You could also watch French films (with French or no subtitles) and try and repeat the dialogue.
Or so, you could try and find a language exchange partner (there are language exchange sites). Looking can be soul destroying - I tried a number of people over the years and have only just found a good one. He speaks English for 30 minutes and I correct him. Then I speak Hungarian and he corrects me.
Practice "shadowing": pick a video or audio in French and try to say what the speaker is saying at the same time as the speaker (singing along with a song is another version of this). Just go a sentence or 2 at a time.
Youtube videos and podcasts can be good sources for the audios. The Mango ap (available for free from many library systems) also generally has good audio files.
As for the pronunciation, you are lucky French has some rules and if you learn them, you will have no problems. Note that, as in every language, you are not aiming to accent but to pronunciation. That means that all you want is to pronounce words right, slowly and clearly, no matter if you sound or not like a native (although it would be really nice if you would xD. I don't, but French undertand me without problems). You can look for some useful sites which basically contain every pronunciation rule (about stressing, the letter "r", the letters "m" and "n", the final syllable and whether it is prnounced or not etc.). Here is a link I found by a quick search: http://www.interactive-audiotexts.com/french_grammar/pronunciation_guide.php. French is not like English; in the latter, you have no absolutely no sign how a word is pronounced (i.e. why is the verb "to live" pronounced differently than the adjective "live"? xD). Once you learn the rules, buy a French book and start reading it out loud; it will help a lot. Listen to french music, watch french YouTube, french series and french films. It is all about practice. Duolingo cannot all by itself bring you to a high level. Happy learning!