I want to impress the ISFJ in a friendship/romantic/work way. We are currently friends and co-workers, but I want to be more than just friends.
The best way to impress anyone you're interested in is to bend your core essence to match what the other person wants, compromise your personal ideals, learn manipulative psychological tactics, and subconsciously lie to yourself and the other person about who you are. Do so without regard to the undue stress and exhaustion you place upon yourself by trying to put up a facade for the entire duration of your relationship, and, of course, any of the harsh potential and deeply personal consequences of those actions.
But I would like to know how to impress the ISFJ, thank you.
Engage him/her in a conversation, possibly work related. Tell him/her in advance that you don't have much time because of [whatever reason]. Be competent and polite while showing a slight disinterest. Throw hints at things you've said or done which ISFJs usually find valuable - family related, for example. Do not appear to be boasting, present the story as if you'd expose a vulnerability to him/her. Don't break eye contact, but try to maintain an easy-going vibe. Ask for his/her help in a future project you're planning (independently) and make sure you keep some of the topics open-ended thus allowing him/her to come back to you if she feels like it. Treat your common acquaintances well and make sure he/she hears about it. Be helpful, be cool, do not invade his/her personal space, use casual body language. Show that you're always ready to walk away and that you have a stable place in your social circle. Make remarks about your current environment without trying hard to observe it, do not laugh at your own jokes. Speak slowly and with enthusiasm. Take note of, but disregard any possible personal attack directed at you.