Flying is basically a skill. With that in mind, all skills are developed through constant practice.All of the great pilots have been successful with their proficiency due to constant practice. However,due to financial reasons, we could not fly all the time. The next best thing that you can do is what we call in the airforce- "bunkfly". It is basically imagining what you would do from pre-flight, cockpit, starting, taxi/run-up, take-off,climb,cruise,descent,landing, missed approaches and shutdown..you could do this while sitting in a chair with your checklist in hand or lying down in your bunks(bed), hence the term....it will really helped a lot for bunkflying will help you when you strapped on.the procedures will be imbibed in your system....MS flight simulator programs also help in terms with your instrument proficiency especially in cross-checks.
on holding altitude-basically procedural,all you have to do is feel the yoke and not fight it.as you may have learned, use the trim to relieve control pressure.cross check your attiutde indicator and altimeter for this will give you the real picture of the attitude of the aircraft..dont rely too much on your VVI/VSI for this instrument has a slight lag or you will be doing broncos in the air if youre trying to zero it.you use this instrument for confirmation with the other two instruments.
radio phraseologies-think before speaking....when called by the controller especially if given instructions,the safest thing to do is read back what he/she said.follow the ABCs of radio phraseology-Accurate,Brief,Concise..
about your instructors, if they are not very helpful,change them....we have a saying at flight school-"if the student failed to learned,the instructor failed to teach"...you have the right to ask them especially if they are paid to teach the rudiments of flight....
dont worry, your time is more than enough for the solo phase, i soloed the cessna 172 in 15 hours...just study your procedures and bunkfly,you will be fine