remember, ASL is a very visual language, so we communicate more with our body language and facial expression than actually with our hands. when in doubt, try to "act out" a word or provide an opposite, or associated word. Your facial expressions will communicate a large portion of what you are trying to say. If your face says nothing while you try to sign the word "yucky", it will be difficult to understand, even if the sign is correct, but if your face says "yucky", your conversation partner is more likely to understand, even if the sign is exactly correct, and they may even be able to provide a correction. When I don't know a sign i make a confusedy face with an "I don't know" kind of body language and then if context isn't enough, i spell it out.
If you make a mistake, visually wipe out the word as if you are writing it in the air, which you technically are doing, and make the face that says "oops! i screwed that up, let me start again"
When reading fingerspelled words, do not memorize each letter and then try to put it together. Doesn't work. Do what you do with written words, sound it out as you encounter the letters. Same with fingerspelling. Don't spell out V-E-R-O-N-I-C-A as it is spelled out to you. Instead, observe the name as it is spelled out and forms sounds ve-ron-ick-a.
Resist the urge to stare at the hands, when being signed to. Focus on the face and see the hands in your peripheral vision, or you will miss a lot and have difficulty mentally connecting.
And, never be afraid to ask for someone to repeat an important word, or to ask people to slow down. People tend to sign and fingerspell at THEIR speed, and that speed will often be faster, or slower than your speed, so the words "slower' and "again" need to be in your vernacular early. And just understand that you are going to miss words here and there, but if you can follow the essential ideas being conveyed, you will be able to follow.