You may wish to follow another way. Instead of play exercises, search and choose a piece you like and may offer to you a "gain" of technique. For example: if you wish to run scales, you have Mozart sonata KV 545 in C Major, 1º movement. Here, you may also train harps. If you wish to train thirds, you have, for example, Mozart Variations "La belle Françoise". If you desire to develop
hands coordination, dexterity, touch and tone, you may try (I almost will say, you must try Two voices Bach inventions (wich will give you musical knowlege, too). These are only examples, you may choose what you wish. So, instead of "mechanical", you are playing good music and gaining sensibility and time. If possible, avoid those pieces played by everybody, stile "fur elise", "moonlight", etc... (but this is only a personal opinion). Before playing something, see what and where are specific dificulties and try to play this bar ou these few bars untill you play them well. But only <> 20 minutes for each kind of dificulty. Then, stop and "sleep". Next day, you`ll see you have a gain. This way, you dont loose your time with exercises, you are "making" allways music. Best wishes - Rui