The best place to start when learning to develop Power BI solutions is to review the logical architecture your Data Visualization projects will have. There are many moving parts and pieces to a Power BI solution, especially when looking at the varied data sources you can use. From on-premises to web-based, from public to confidential, you must make sure you expose your data securely. Having a good clear architecture will help you achieve a not only a good solution but also a secure one. The following article will show you how you can architect your own solution.
There is a very active community around PowerBI with many sites specializing in different aspects of the product. The following 4 resources are ones I always fall back on recommending that provide both beginner and advanced users learning resources.
The date dimension is the table that controls your time analysis and the most important to get right, especially with PowerBI and other visualization tools. Having various tags and descriptors that aid in your analysis gives your end users several options in creating their visualizations in addition to a base for DAX time intelligence calculations.
There are times when, as a consultant, you have to produce a demo or training database that has no relation to the client that you are doing the work for. This can be due to security or confidentiality of the data. I try to produce training and samples that at least have realistic values so that the people involved have a frame of reference.
If you have an excel table that is built for data entry, it may not be in the best format for data analysis or your data model. By using Query Editor, you can keep the original table and create a version that you can use for analysis as a dimensional fact table.